Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

Methods and devices are provided for improved deposition systems. In one
non-limiting example, a deposition system is provided for use with a
solution and a substrate. The system comprises of a solution deposition
apparatus; at least one heating chamber; at least one assembly for
holding a solution over the substrate; and a substrate curling apparatus
for curling at least one edge of the substrate to define a zone capable
of containing a volume of the solution over the substrate. In another
embodiment of the present invention, a deposition system for use with a
substrate, the system comprising a solution deposition apparatus; at
heating chamber; and at least assembly for holding solution over the
substrate to allow for a depth of at least about 0.5 microns to 10 mm.

Claims:

1. A buffer layer deposition system for use with a solution and an
exposed surface of a solar cell absorber layer disposed on a continuous
flexible substrate for manufacturing solar cells, the system comprising:
a solution deposition apparatus; at least one heated processing bed; at
least one assembly for holding a solution over the substrate; a substrate
curling apparatus for curling at least one edge of the substrate to
define a zone capable of containing a volume of the solution over the
substrate, wherein the assembly curls at least two edges of the
substrate; and each of the edges having at least one sealing member in
contact with the edge and configured to extend into solution on the
substrate.

2. The system of claim 1 wherein the assembly for holding solution over
the substrate to allow for a depth of at least about 1 mm to about 5 mm.

3. The system of claim 1 wherein the curling apparatus curls opposing
edges of the substrate.

4. The system of claim 3 wherein the curling apparatus is configured to
transition a planar substrate to a substrate with curls along two edges,
wherein the transition occurs over a distance sufficient prevent
permanent deformation of the substrate when the substrate is uncurled.

5. The system of claim 1 further comprising using a deposition station to
deposit one component of the solution to clean the substrate prior to
heating the solution to processing temperature.

6. The system of claim 1 wherein the solution comprises a precursor for
forming a junction partner for a group IB-IIIA-VIA absorber layer.

8. The system of claim 1 wherein the solution comprises of a Group IIB
ionic species is obtained from an aqueous solution of one or more of the
following: sulfate, acetate, bromide, fluoride, chloride, iodide,
hydroxide, nitrate, oxalate, citrate, phosphate, tungstate, or hydrates
of the Group IIB species.

9. The system of claim 1 wherein the solution comprises of a Group VIA
ionic species is obtained from an aqueous solution of one or more of the
following: oxides, halides, sulfates, nitrates, or ureates of the Group
VIA species.

10. The system of claim 1 wherein the solution has a pH of from about 9
to about 14.

11. The system of claim 1 wherein the solution has a pH of from about 11
to about 12.

12. The system of claim 1 wherein the assembly for holding solution is at
least partially contained in the heating chamber.

13. The system of claim 1 wherein the solution comprises a precursor for
forming a Group IIB-VIA junction partner.

15. The system of claim 1 wherein the solution comprises of a Group IIB
ionic species is obtained from an aqueous solution of one or more of the
following: sulfate, acetate, bromide, fluoride, chloride, iodide,
hydroxide, nitrate, oxalate, citrate, phosphate, tungstate, or hydrates
of the Group IIB species.

16. A buffer layer deposition system for use with a solution and an
exposed surface of a solar cell absorber layer disposed on a continuous
flexible substrate for manufacturing solar cells, the system comprising:
a substrate curling apparatus for curling at least one edge of the
substrate to define a zone capable of containing a volume of the solution
over the substrate, wherein the assembly curls at least two edges of the
substrate; and each of the edges having at least one sealing member to
minimize loss of process gas above the substrate.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Application
Ser. No. 61/333,241 filed May 10, 2010. All applications are fully
incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

[0002] This invention relates generally to deposition systems, and more
specifically, solution deposition systems for use in forming photovoltaic
devices.

BACKGROUND OF THE INVENTION

[0003] Solar cells and solar modules convert sunlight into electricity.
These electronic devices have been traditionally fabricated using silicon
(Si) as a light-absorbing, semiconducting material in a relatively
expensive production process. To make solar cells more economically
viable, solar cell device architectures have been developed that can
inexpensively make use of thin-film, light-absorbing semiconductor
materials such as copper-indium-gallium-di-(sulfo-selenide, Cu(In, Ga)(S,
Se)2, also termed CI(G)S(S). This class of solar cells typically has
a p-type absorber layer sandwiched between a back electrode layer and an
n-type junction partner layer. The back electrode layer is often Mo,
while the junction partner is often CdS. A transparent conductive oxide
(TCO) such as zinc oxide (ZnOx) typically doped with aluminum is
formed on the junction partner layer and is typically used as a
transparent electrode. CIS-based solar cells have been demonstrated to
have power conversion efficiencies exceeding 19%.

[0004] High throughput production methods are in development to
manufacture this type of thin-film photovoltaic device. As improvements
are made for high throughput production of the absorber layer in such
thin-film devices, similar advances need to be made with regards the
deposition or formation of the junction partner layer to prevent
bottlenecking of the production process.

[0005] It should be understood, however, that the materials used for
forming the junction partner can contain toxic material and difficulties
are encountered in improving the manufacturing system. One process for
forming the junction partner involves using Group II-VI compounds such as
CdS. The CdS used in the formation process may create hazardous waste
by-products, thus increasing processing costs. Known processes are also
inefficient or unreliable in creating a system with high throughput and
high yield. Some known systems either use too much starting material,
much of which is wasted during production. Others use systems that may be
susceptible to imperfections in the underlying substrate that may cause
non-uniform deposition of the junction partner material over a wide web.
Therefore, a need exists in the art for an improved junction partner
deposition system.

SUMMARY OF THE INVENTION

[0006] Embodiments of the present invention address at least some of the
drawbacks set forth above. The present invention provides for the
improved deposition system for group IIB-VIA materials. Although not
limited to the following, these improved module designs are well suited
for roll-to-roll, in-line processing equipment. It should be understood
that at least some embodiments of the present invention may be applicable
to any type of solar cell, whether they are rigid or flexible in nature
or the type of material used in the absorber layer. Embodiments of the
present invention may be adaptable for roll-to-roll and/or batch
manufacturing processes. At least some of these and other objectives
described herein will be met by various embodiments of the present
invention.

[0007] In one embodiment of the present invention, a deposition system is
provided for use with a solution and a substrate. The system comprises of
a solution deposition apparatus; at least one heating chamber; at least
one assembly for holding a solution over the substrate; and a substrate
curling apparatus for curling at least one edge of the substrate to
define a zone capable of containing a volume of the solution over the
substrate. Although the term substrate is used, it should be understood
that the substrate may have materials formed in it already at the time it
is processed by embodiments of the current invention. Thus, the present
embodiment may be depositing a buffer layer material from a solution to
an exposed surface of a solar cell absorber layer of a workpiece or
substrate for manufacturing of solar cells. In one embodiment, the
curling apparatus is heated to assist in curving the foil.

[0008] In another embodiment of the present invention, a deposition system
for use with a substrate, the system comprising a solution deposition
apparatus; at heating chamber; and at least assembly for holding solution
over the substrate to allow for a depth of at least about 0.5 microns to
10 mm. In one embodiment, the substrate comprises a magnetic component
and a non-magnetic component.

[0009] In yet another embodiment of the present invention, a deposition
system is provided for use with a solution and a substrate. The system
comprises of a solution deposition apparatus; at least one heating
chamber; at least one assembly for holding a solution over the substrate;
and a substrate curling apparatus for curling at least one edge of the
substrate to define a zone capable of containing a volume of the solution
over the substrate.

[0010] It should be understood that any of the embodiments herein may be
adapted to have one or more of the following features. In one embodiment,
the assembly curls at least two edges of the substrate. Optionally, the
assembly for holding solution over the substrate to allow for a depth of
at least about 0.5 microns to about 10 mm. Optionally, the assembly for
holding solution over the substrate to allow for a depth of at least
about 1 mm to about 5 mm. Optionally, the curling apparatus curls
opposing edges of the substrate. Optionally, the curling apparatus is
configured to transition a planar substrate to a substrate with curls
along two edges, wherein the transition occurs over a distance sufficient
prevent permanent deformation of the substrate when the substrate is
uncurled. Optionally, the curling apparatus is configured to transition a
planar substrate to a substrate with curls along two edges over a
distance of at least 4 inches. Optionally, the curling apparatus is
configured to transition a planar substrate to a substrate with curls
along two edges over a distance of at least 6 inches. Optionally, the
curling apparatus creates curls of sufficient height to contain the
volume of solution therein without allowing the solution to spill over an
upper of the curl. Optionally, the assembly for holding solution further
comprises of an uncurling apparatus for uncurling at least two edges of
the substrate to return the substrate to a substantially planar
configuration. Optionally, the curling apparatus comprise of a web guide.
Optionally, the curling apparatus comprise of a shaped web guide.
Optionally, the solution deposition apparatus comprises of a spray
deposition system to deposit the solution over the substrate. Optionally,
the solution deposition apparatus comprises of an ultrasonic spray
deposition system to deposit the solution over the substrate. Optionally,
the substrate comprises of a flexible material. Optionally, the substrate
comprises of a metal foil. Optionally, the solution comprises a precursor
for forming a junction partner for a group IB-IIIA-VIA absorber layer.
Optionally, the solution comprises a precursor for forming a Group
IIB-VIA junction partner. Optionally, the solution comprises a precursor
for forming a junction partner selected from the group consisting of:
cadmium sulfide (CdS), zinc sulfide (ZnS), zinc hydroxide, zinc selenide
(ZnSe). Optionally, the solution comprises of a Group JIB ionic species
is obtained from an aqueous solution of one or more of the following:
sulfate, acetate, bromide, fluoride, chloride, iodide, hydroxide,
nitrate, oxalate, citrate, phosphate, tungstate, or hydrates of the Group
IIB species. Optionally, the solution comprises of a Group VIA ionic
species is obtained from an aqueous solution of one or more of the
following: oxides, halides, sulfates, nitrates, or ureates of the Group
VIA species. Optionally, the solution has a pH of from about 9 to about
14. Optionally, the solution has a pH of from about 11 to about 12.
Optionally, the solution has a pH of from about 12 to about 13.
Optionally, the solution has a pH of from about 11 to about 13.
Optionally, the assembly for holding solution is at least partially
contained in the heating chamber.

[0011] In one embodiment of the present invention, a method is provided
for depositing a buffer layer material from a solution to an exposed
surface of a solar cell absorber layer disposed on a continuous flexible
workpiece for manufacturing solar cells as the continuous flexible
workpiece is advanced through a roll-to-roll system, comprising:
advancing a section of the continuous flexible workpiece from a supply
roll and having a flat shape onto a heated plate including a cavity area,
wherein the cavity area of the heated plate is configured to elastically
alter the section of the continuous flexible workpiece into a curved
shape that conforms to the cavity area of the continuous flexible
workpiece; flowing a supply solution over an exposed surface of the solar
cell absorber layer of the curved-shape section of the continuous
flexible workpiece, wherein the supply solution is maintained at a first
temperature before flowing into the section of the continuous flexible
workpiece that conforms to the cavity area of the heated plate with the
curved shape and wherein the supply solution includes all the chemical
components of the buffer layer material; heating, to a second temperature
which is higher than the first temperature, the continuous flexible
workpiece and the solar cell absorber layer using the heated plate when
the section of the continuous flexible workpiece is within the cavity
area and conforming to the cavity area with the curved shape, wherein the
heating of the continuous flexible workpiece and the absorber layer cause
the transfer of heat from the solar cell absorber layer to at least a
portion of the solution that is in contact with the exposed surface of
the solar cell absorber layer and to cause depositing of the buffer layer
material within the solution onto the exposed surface of the solar cell
absorber layer; and moving the section of the continuous flexible
workpiece away from the cavity areas of the heated plate so that the
section of the continuous flexible workpiece flattens.

[0012] A further understanding of the nature and advantages of the
invention will become apparent by reference to the remaining portions of
the specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a cross-sectional view of a photovoltaic device according
to one embodiment of the present invention.

[0014] FIG. 2 shows a processing system according to one embodiment of the
present invention.

[0015]FIG. 3 shows a processing system according to another embodiment of
the present invention.

[0016] FIG. 4 shows top down view of a processing system according to
another embodiment of the present invention.

[0017] FIG. 5 shows cross-sectional view of a processing system according
to one embodiment of the present invention.

[0018] FIG. 6 shows a processing system according to another embodiment of
the present invention.

[0019] FIG. 7 shows a processing system according to another embodiment of
the present invention.

[0021] FIG. 9 shows a cross-sectional view of one embodiment of a
processing system configured to curl one or more edges of a substrate.

[0022] FIG. 10 through 11B show various mechanisms for use for curling one
or more edges of a substrate.

[0023] FIGS. 12A-12C show various configurations for a substrate with
upwardly shaped edges.

[0024] FIGS. 13 and 14 are top down views of a processing system showing
locations of the substrate shaping assemblies according to embodiments of
the present invention.

[0025] FIGS. 15 through 19 are side views of processing systems according
to various embodiments of the present invention.

[0026] FIG. 20 shows a top down view of one portion of a substrate
according to the present invention.

[0027] FIGS. 21 and 22 show a cross-web view of the substrate according to
embodiments of the present invention.

[0028] FIGS. 23A and 23B show a cross-web view of the substrate according
to embodiments of the present invention.

[0029] FIGS. 24 through 28 show various methods for edge sealing against
the lateral edges of the substrate according to embodiments of the
present invention.

[0030] FIGS. 29 and 30 show embodiments of the present invention with
stirring mechanisms along the substrate path.

[0031] FIG. 31 shows one embodiment of a vacuum belt suitable for use with
an embodiment of the present invention.

[0032] FIGS. 32A-32C show various embodiment of a vacuum guide, bed, or
belt according to embodiments of the present invention.

[0033] FIG. 33 shows a web path through one embodiment of processing
system according to the present invention.

[0034] FIGS. 34 to 39 show top down schematics of various processing
systems according to embodiments of the present invention.

[0035] FIGS. 41 to 44 show down-web cross-sectional views of portions of
the curved substrate with various devices for sealing the atmosphere over
the fluid on the substrate according to embodiments of the present
invention.

[0036] FIGS. 45 to 47 show side schematic views of various processing
systems according to embodiments of the present invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0037] It is to be understood that both the foregoing general description
and the following detailed description are exemplary and explanatory only
and are not restrictive of the invention, as claimed. It may be noted
that, as used in the specification and the appended claims, the singular
forms "a", "an" and "the" include plural referents unless the context
clearly dictates otherwise. Thus, for example, reference to "a material"
may include mixtures of materials, reference to "a compound" may include
multiple compounds, and the like. References cited herein are hereby
incorporated by reference in their entirety, except to the extent that
they conflict with teachings explicitly set forth in this specification.

[0038] In this specification and in the claims which follow, reference
will be made to a number of terms which shall be defined to have the
following meanings:

[0039] "Optional" or "optionally" means that the subsequently described
circumstance may or may not occur, so that the description includes
instances where the circumstance occurs and instances where it does not.
For example, if a roller optionally contains a feature for a thermally
conductive film, this means that the conductive film feature may or may
not be present, and, thus, the description includes both structures
wherein a roller possesses the conductive film feature and structures
wherein the film feature is not present.

[0040] Photovoltaic Device Structure

[0041] Referring now to FIG. 1, one embodiment of such a photovoltaic
device 10 will now be described. Although the present embodiment is
described in the context of a thin-film group IB-IIIA-VIA device, it
should be understood that other types of photovoltaic devices may also be
produced using the junction partner formation techniques described
herein.

[0042] As seen in FIG. 1, the structure of a photovoltaic device 10
according to the present invention includes a base substrate 12, an
optional intermediate layer 13, a base or back electrode 14, a p-type
absorber layer 16 incorporating a film of the type described above, a
n-type junction partner semiconductor thin film 18, and a transparent
electrode 20. By way of example, the base substrate 12 may be made of a
metal foil, a polymer such as polyimides (PI), polyamides,
polyetheretherketone (PEEK), Polyethersulfone (PES), polyetherimide
(PEI), polyethylene naphtalate (PEN), Polyester (PET), related polymers,
or a metallized plastic. By way of nonlimiting example, related polymers
include those with similar structural and/or functional properties and/or
material attributes. The base electrode 14 is made of an electrically
conductive material. By way of example, the base electrode 14 may be of a
metal layer whose thickness may be selected from the range of about 0.1
micron to about 25 microns. An optional intermediate layer 13 may be
incorporated between the electrode 14 and the substrate 12. The
transparent electrode 20 may include a transparent conductive layer 19
and a layer of metal (e.g., Al, Ag, Cu, or Ni) fingers 21 to reduce sheet
resistance.

[0043] In one embodiment, the base substrate 12 may be a metal foil made
of a material such as but not limited to stainless steel, copper,
aluminum, nickel, molybdenum, or the like. In one embodiment, aluminum is
used with a molybdenum base electrode. Aluminum and molybdenum, however,
can and often do inter-diffuse into one another, especially upon heating
to elevated temperatures as used for absorber growth, with deleterious
electronic and/or optoelectronic effects on the device 10. Furthermore
aluminum can diffuse though molybdenum into layers beyond e.g. CIG(S). To
inhibit such inter-diffusion, an intermediate, interfacial layer 13 may
be incorporated between the aluminum foil substrate 12 and molybdenum
base electrode 14. The interfacial layer may be composed of any of a
variety of materials, including but not limited to chromium, vanadium,
tungsten, and glass, or compounds such as nitrides (including but not
limited to titanium nitride, tantalum nitride, tungsten nitride, hafnium
nitride, niobium nitride, zirconium nitride, vanadium nitride, silicon
nitride, or molybdenum nitride), oxynitrides (including but not limited
to oxynitrides of Ti, Ta, V, W, Si, Zr, Nb, Hf, or Mo), oxides, and/or
carbides. The material may be selected to be an electrically conductive
material. In one embodiment, the materials selected from the
aforementioned may be those that are electrically conductive diffusion
barriers. The thickness of this layer can range from 10 nm to 50 nm or
from 10 nm to 30 nm. Optionally, the thickness may be in the range of
about 50 nm to about 1000 nm. Optionally, the thickness may be in the
range of about 100 nm to about 750 nm. Optionally, the thickness may be
in the range of about 100 nm to about 500 nm. Optionally, the thickness
may be in the range of about 110 nm to about 300 nm. In one embodiment,
the thickness of the layer 13 is at least 100 nm or more. In another
embodiment, the thickness of the layer 13 is at least 150 nm or more. In
one embodiment, the thickness of the layer 13 is at least 200 nm or more.
Optionally, some embodiments may include another layer such as but not
limited to a copper layer, a titanium layer, or other metal layer above
the layer 13 and below the base electrode layer 14. Optionally, some
embodiments may include another layer such as but not limited to a copper
layer, a titanium layer, an aluminum layer, or other metal layer below
the layer 13 and below the base electrode layer 14. This layer may be
thicker than the layer 13. Optionally, it may be the same thickness or
thinner than the layer 13. This layer 13 may be placed on one or
optionally both sides of the aluminum foil (shown as layer 15 in phantom
in FIG. 5). Some embodiments may use an electrically conductive barrier
on side and a non-electrically conductive barrier on the other side.
Other embodiments use the same type of conductivity material on both
sides.

[0044] If barrier layers are on both sides of the substrate 12, it should
be understood that the protective layers may be of the same material or
they may optionally be different materials from the aforementioned
materials. The bottom protective layer 105 may be any of the materials.
Optionally, some embodiments may include another layer 107 such as but
not limited to an aluminum layer above the layer 105 and below the
aluminum foil 102. This layer 107 may be thicker than the layer 103

[0045] In the present embodiment, the structure of the photovoltaic device
10 may include a semiconductor thin film 18 of a complementary charge
type that serves as a junction partner between the compound film and the
transparent conducting layer 19. By way of example, the n-type
semiconductor thin film 18 (sometimes referred to as a junction partner
layer) may include inorganic materials such as cadmium sulfide (CdS),
zinc sulfide (ZnS), zinc hydroxide, zinc selenide (ZnSe), n-type organic
materials, or some combination of two or more of these or similar
materials, or organic materials such as n-type polymers and/or small
molecules. Other types of junction partner material such as
poly(benzimidazobenzophenanthroline ladder) (BBL) may also be used as a
junction partner material according to the present invention. Details
about BBL is provided in copending U.S. patent application Ser. No.
11/409,503 filed Apr. 21, 2006, fully incorporated herein by reference
for all purposes. Layers of these materials may be deposited, e.g., by
chemical bath deposition (CBD) and/or chemical surface deposition (and/or
related methods), to a thickness ranging from about 2 nm to about 1000
nm, more optionally from about 5 nm to about 500 nm, and most optionally
from about 10 nm to about 300 nm. In some embodiments, the thickness may
be in the range of about 10 to about 100 nm. In other embodiments, the
thickness may be in the range of about 15 to about 80 nm. This may also
configured for use in a continuous roll-to-roll and/or segmented
roll-to-roll and/or a batch mode system.

[0046] The transparent conductive layer 19 may be inorganic, e.g., a
transparent conductive oxide (TCO) such as but not limited to indium tin
oxide (ITO), fluorinated indium tin oxide, zinc oxide (ZnO) or zinc oxide
(ZnOx) doped with aluminum, or a related material, which can be
deposited using any of a variety of means including but not limited to
sputtering, evaporation, chemical bath deposition (CBD, electroplating,
sol-gel based coating, spray coating, chemical vapor deposition (CVD),
physical vapor deposition (PVD), atomic layer deposition (ALD), and the
like. Alternatively, the transparent conductive layer may include a
transparent conductive polymeric layer, e.g. a transparent layer of doped
PEDOT (Poly-3,4-Ethylenedioxythiophene), carbon nanotubes or related
structures, or other transparent organic materials, either singly or in
combination, which can be deposited using spin, dip, or spray coating,
and the like or using any of various vapor deposition techniques.
Optionally, it should be understood that a non-conductive layer such as
intrinsic ZnO (i-ZnO) may be used between CdS and Al-doped ZnO.
Optionally, an insulating layer may be included between the layer 18 and
transparent conductive layer 19. Combinations of inorganic and organic
materials can also be used to form a hybrid transparent conductive layer.
Thus, the layer 19 may optionally be an organic (polymeric or a mixed
polymeric-molecular) or a hybrid (organic-inorganic) material. Examples
of such a transparent conductive layer are described e.g., in
commonly-assigned US Patent Application Publication Number 20040187317,
which is incorporated herein by reference.

[0047] Those of skill in the art will be able to devise variations on the
above embodiments that are within the scope of these teachings. For
example, it is noted that in embodiments of the present invention,
portions of the IB-IIIA precursor layers (or certain sub-layers of the
precursor layers or other layers in the stack) may be deposited using
techniques other than microflake-based inks For example precursor layers
or constituent sub-layers may be deposited using any of a variety of
alternative deposition techniques including but not limited to
solution-deposition of spherical nanopowder-based inks, vapor deposition
techniques such as ALD, evaporation, sputtering, CVD, PVD, electroplating
and the like.

[0048] Junction Partner Deposition System

[0049] Referring now to FIG. 2, one embodiment of a junction partner
deposition system will now be described. In this embodiment of the
invention, the deposition system may be a solution deposition system that
occurs in an environment at atmospheric pressures. Optionally, it should
be understood that the deposition system may also be used with vacuum,
low vacuum, and/or sub-atmospheric pressures. Some embodiments may also
use environments at pressures higher than atmospheric pressure.

[0050] FIG. 2 shows a system with a substrate 50 configured for use in an
in-line, roll-to-roll configuration. The substrate 50 may be a coated
metal, coated polymer, coated metallized polymer substrate, or any other
substrate previous described herein. The coating may be a photovoltaic
absorber layer such as but not limited to Cu--In--Ga--Se, Cu--In--Se,
Cu--In--Ga--S, Cu--In--Ga--Se--S, other group IB-IIIA-VIA absorbers,
CdTe, sulfo-salt, group IIB-VIA absorber, or other photovoltaic absorbers
that use a junction partner layer. The photovoltaic absorber layer or
other coating formed on the substrate 50 may be formed from one or more
precursors deposited by any of a variety methods including but not
limited to sputtering, electrodeposition, electroplating, solution
deposition, ALD, evaporation, CVD, PVD, and/or the like. When the term
substrate 50 is discussed herein, it may be a bare substrate or it may be
the substrate with the coating thereon. By way of nonlimiting example,
these absorber layers may also be formed on rigid substrates or flexible
substrates.

[0051] In one embodiment, the substrate 50 is a flexible elongate
substrate such as but not limited to an absorber coated metal foil. In
another embodiment, the substrate 50 is a multi-layered flexible
substrate such as that shown in FIG. 1. Optionally, there may be a
carrier on which discrete or pre-cut substrates comprising the precursor
layers may be placed. The carrier may then carry these discrete or
pre-cut substrates through the processing station(s). As part of the
initial setup, the surface of the substrate to be processed may be
cleaned prior to solution deposition.

[0052] By way of example and not limitation, the junction partner used
with the substrate 50 may be a Group IIB-VIA material. In one embodiment,
the Group IIB ionic species may be comprised of one or more of the
following: cadmium, mercury, zinc, cadmium, mercury or zinc which may be
provided by one or more solutions of the following: sulfate, acetate,
bromide, fluoride, chloride, iodide, hydroxide, nitrate, oxalate,
citrate, phosphate, tungstate, hydrates or combinations thereof. The
Group VIA ionic species comprises oxygen, sulfur, selenium, tellurium,
polonium, or combinations thereof. The Group VIA ionic species is
optionally obtained from an aqueous solution of oxides, halides,
sulfates, nitrates, or ureates of the Group VIA species. The liquid
coating composition optionally further comprises a solvent such as water,
optionally deionized water. The liquid coating composition optionally has
a pH of from about 9 to about 14, more optionally from about 10 to about
13 and most optionally from about 11 to about 12.

[0053] In one embodiment, a CdS layer is formed on substrate 50 by a
solution deposition process. More specifically, in this embodiment, a
solution containing cadmium acetate (Cd(CH3 COO)2), thiourea
(NH2 CSNH2), ammonium acetate (CH3 COONH4) and
ammonia is prepared. In this present embodiment, the concentration of the
cadmium acetate in the solution was 0.001M, the concentration of the
thiourea was 0.005M, the concentration of the ammonium acetate was 0.01M
and the concentration of the ammonia was 0.4M. The substrate coated in
this solution to form a CdS layer on the substrate. This is purely
exemplary and is non-limiting.

[0054] A variety of solution-based coating techniques may be used to apply
the above liquids including but not limited to wet coating, spray
coating, spin coating, doctor blade coating, contact printing, top feed
reverse printing, bottom feed reverse printing, nozzle feed reverse
printing, gravure printing, microgravure printing, reverse microgravure
printing, comma direct printing, roller coating, slot die coating,
meyerbar coating, lip direct coating, dual lip direct coating, capillary
coating, ink jet printing, jet deposition, spray deposition, ultrasonic
spray deposition, and the like, as well as combinations of the above
and/or related technologies. The surface of the substrate 50 can be
modified by the addition of a wetting agent to the solution, such as but
not limited to glycerine. The liquid may also be a dispersion or ink
containing the aforementioned materials. Depending on such surface
tension, application of the liquid onto the substrate may optionally be
conducted upside down.

[0055] Referring still to FIG. 2, this embodiment shows that a spray
technique is used to apply the liquid coating to the substrate 50. In
this embodiment, the solution may be a mixture of 0.005-0.01M CdSO4
solution with 2M of NH4OH to pH of about 12. Optionally, the solution may
be a mixture of cadmium sulfate is between about 0.001 to about 0.008
mole/liter. Optionally, the solution may be a mixture of cadmium sulfate
is between about 0.002 to about 0.005 mole/liter. Optionally, a 0.3-0.5M
thiourea solution is included. Optionally, the thiourea concentration is
between 0.1-0.6 mole/liter. Optionally, the thiourea concentration is
between 0.2-0.5 mole/liter. FIG. 2 shows that this embodiment uses a
spraying assembly 60 configured to spray material onto the substrate 50.
By way of example and not limitation, the spray assembly 60 may use a
single nozzle, two nozzles, or multiple nozzles to spray liquid across
the width of the substrate 50. One or more of the nozzles may be
ultrasonic nozzles. Ultrasonic nozzles are commercially available from
manufacturers such as J D Ultrasonics of the United Kingdom. Optionally,
the nozzles may be dual jet nozzles that are configured for atomizing
liquid across a wide web such as that available from Wilson Spray Nozzle
of Singapore. There may be one or more these wide web nozzles in assembly
60. Optionally, one or more of the nozzles may be a vortex nozzle,
wherein the flow from the nozzle is such that a vortexing flow exits the
nozzle to define a cone-shaped spray. Optionally, wide web and vortex
nozzles may be used in combination. The spray assembly 60 may be
sufficient to spray across a substrate 50 that may have a width of
greater than 0.5 meters. Optionally, the spray assembly 60 may be
sufficient to spray across a substrate 50 that may have a width of
greater than 1.0 meters. Optionally, the spray assembly 60 may be
sufficient to spray across a substrate 50 that may have a width of
greater than 2.0 meters. Optionally, the spray assembly 60 may be
sufficient to spray across a substrate 50 that may have a width of
greater than 3.0 meters.

[0056] It should also be understood that the temperature of the solution
or dispersion being deposited and/or that of the substrate may also be
controlled. In one embodiment, the container containing this solution was
put in a hot water bath kept at about 85 degree C. prior to deposition
and is deposited on a substrate at a lower temperature. In some
embodiments, the substrate is at ambient temperature, or heated but to a
temperature less than or equal to the temperature of the solution or
dispersion to be deposited. Optionally, both the solution and the
substrate 50 are at substantially the same temperature. In one
embodiment, neither the solution or the substrate 50 are heated and both
are at ambient temperatures. In other embodiments, the substrate 50 may
be heated from ambient to about 60 to about 90° C. In other
embodiments, the substrate 50 may be heated from ambient to about 50 to
about 90° C. In other embodiments, the substrate 50 may be heated
from ambient to about 40 to about 100° C. In other embodiments,
the solution or dispersion may actually be chilled or cooled to be below
ambient temperature.

[0057] In another aspect, the amount of solution applied may be either a
thin layer or it may be sufficient to create a bath of a depth of about
0.5 mm to about 5 mm in depth. Optionally, the bath may be about 0.5
microns to about 10 mm in depth. A shallow bath allows for sufficient
coverage of the entire target surface of the substrate 50 while not
substantially under-utilizing the raw material. The bath above the
substrate 50 may be contained above the substrate 50 against a slidable
seal and/or a movable seal. Optionally, the substrate 50 passes through a
bath of the solution, wherein the substrate 50 may have a backside layer
that can be removed.

[0058] Referring still to FIG. 2, a second deposition assembly 70 (shown
in phantom) may also be used. This may be the same type of ultrasonic
nozzle used in the solution deposition assembly 60. Optionally, it may
one of the other types of deposition system such as but not limited to a
vortex, wide-web, or other nozzle type different from the nozzle used in
the solution deposition assembly 60. Optionally, the second deposition
assembly 70 may include one or more of the following: wet coating, spray
coating, spin coating, doctor blade coating, contact printing, top feed
reverse printing, bottom feed reverse printing, nozzle feed reverse
printing, gravure printing, microgravure printing, reverse microgravure
printing, comma direct printing, roller coating, slot die coating,
meyerbar coating, lip direct coating, dual lip direct coating, capillary
coating, ink jet printing, jet deposition, spray deposition, and the
like, as well as combinations of the above and/or related technologies.
The solution from assembly 70 may be the same as that from assembly 60 or
it may be a component used in the process such as the thiourea solution
or the like.

[0059] It should be understood that in some embodiments, there may be more
than two deposition sources 60 and 70. Some embodiments may have three or
more. Each may be depositing just one component of the material in the
processing solution. Some may be depositing mixtures. Some embodiments
may use a combination (some sources depositing just one component, while
another source depositions mixtures of one or more). It should also be
understood that in some embodiments, the solutions, components, or other
material from deposition sources 60 and 70 may all be at temperatures
higher than that of the substrate, the same as the temperature of the
substrate, or at temperatures lower than that of the substrate.
Optionally, only one of the deposition sources is depositing at
temperatures higher than that of the substrate. Optionally, only one of
the deposition sources is depositing at temperatures the same as that of
the substrate. Optionally, only one of the deposition sources is
depositing at temperatures lower than that of the substrate. The sequence
may also be varied such as but not limited to a cadmium salt solution
first and then thiourea or other S solution later. Some embodiments may
add one or more other complexing agents. The sequence may be varied with
the S solution deposited first and then followed by the cadmium salt
solution and any other components. Some may involve a combination of wet
deposition and dry deposition processes such as a liquid S solution with
cadmium salt nanoparticles added at a different station. Of course, the
type of deposition may also be varied such as but not limited to slot die
deposition followed by a predefined time delay of a spray deposition of
another component or vice versa. Any of the multi-deposition source
systems may be adapted for use with any of the embodiment of the
processing system described herein.

[0060] As seen in FIG. 2, after solution deposition by assembly 60 and/or
70, the substrate 50 enters an oven 80 for heating the solution to enable
film growth or formation. In one embodiment, the over 80 is used to heat
the substrate to between about 65 to about 90C. Optionally, some
embodiments, may heat to higher temperatures such as about 90 to about
130C. A variety of ovens may work. In one embodiment, the oven 80
comprises of an infrared oven is used to heat the substrate 50 and the
solution over the substrate 50. Infrared ovens are available from a
variety of manufacturers including Glenro Inc. of Paterson, N.J. Other
embodiments may use muffles wherein the heating elements are located
outside the tube furnace or muffle through which the substrate passes.
The heating elements heat the muffle, which in turn heats the substrate.
Some embodiments may only include heating element on one side of the oven
80 (e.g. top) or only on the other side (e.g. bottom). In one embodiment,
the group IIB-VIA material over the substrate 50 may have a cured
thickness of about 20 to about 100 nanometers. Optionally, the thickness
may be between about 100 to about 150 nanometers.

[0061] After passing through the oven 80, the substrate 50 reaches a
cleaning station 90. This cleaning system 90 may use a pressure spray of
liquid such as but not limited to deionized water to remove unused or
uncured solution applied to the substrate 50. The wash off from the
pressure spray is collected and the waste liquid contained or processed
for proper removal.

[0062] Optionally, a second cleaning station 100 is included. This may be
an additional washing station similar to the cleaning station 90, it may
be an air knife or other source to dry the substrate 50, or it may be
cleaning system using some other type of cleaning solution. The cleaning
and/or drying may occur on only one side of the substrate 50 or it may be
from the underside or other directions as indicted by stations 92 and 102
in phantom. Optionally, it may be a combined heating and air dry station
to remove un-wanted material from the surface of the substrate and to
prepare the substrate for the next stage of processing. In some
embodiments, the heating may occur after the air drying and may use an
infrared heating to increase the substrate temperature and to prepare it
for the next layer to be deposited on the photovoltaic device. In one
embodiment, the substrate 50 after the various processes above, is heated
to about 100C or higher at 2 meters per minute to dry the web or
substrate 50 and to prepare it for the next layer.

[0063] Referring now to FIG. 3, another embodiment of the present
invention will now be described. This embodiment shows a junction partner
deposition system 130 with a solution deposition by assembly 60 and/or
70. The oven 80 is used to heat the solution deposited on the substrate
50 to from the assembly 60 and/or 70. This embodiment of the junction
partner deposition system includes a vacuum pull belt system 140 which
will help flatten the substrate 50 during the processing. This is
particularly helpful as some wider flexible substrates 50 after
deposition of semiconductor or other absorber material will curl and
assume non-planar configurations without force or substrate guides to
help flatten the substrate 50. Vacuum pull belt systems are available
from manufacturers such as Kliklok-Woodman of Decatur Georgia. Some
systems may use an articulated floating vacuum pull belt arrangement as
described in U.S. Pat. No. 5,715,656 and fully incorporated herein by
reference for all purposes.

[0064] In this embodiment, the vacuum pull belt system 140 extends outside
the oven 80. Optionally, in other embodiments, the vacuum pull belt
system 140 may extend only within the boundaries of the oven 80. As seen
in FIG. 3, the spray of the solution may occur over the system 140 by way
of the spray assembly 60 or it may occur at a location of the substrate
50 spaced away from the belt system 140 as indicated by a spray assembly
located at position 70.

[0065] FIG. 4 shows yet another embodiment wherein a moving seal systems
160 and 162 which may be alongside the areas where the solution is
deposited on the substrate 50. FIG. 4 is a top down view of the substrate
50 and the seals of the systems 160 and 162 will form side walls against
the substrate 50 that allows the bath to be formed over the substrate 50.
In one embodiment, the seals of the systems 160 and 162 will also keep
the bath or layer of solution on only one side of the substrate 50. The
systems 160 and 162 may also be configured to have seals that move with
the substrate 50. Other embodiments may have stationary seals that allow
the substrate to slide along against it. Some embodiments may also
include a dip in the substrate path (see FIG. 33) to help prevent the
fluid or solution from flowing too far downweb or upweb. Scrubbing units
170 and 172 may also be included to clean the surface of the seal to
remove and undesired build up that may prevent a good seal against the
substrate 50. Other embodiments may use the units 170 and 172 to apply
sealant to help the seal against the substrate 50.

[0066] Still further embodiments may use two back-to-back substrates 50 to
allow for higher utilization. To avoid waste or undesired processing, two
substrates may be attached together "back-to-back" to form a dual
substrate having, in effect, two front sides with the back sides
protected against undesired treatment. Preferably, the substrates are
attached in a manner that allows them to be separated from each other
after processing. By way of example the substrates may be attached with a
low-strength adhesive or electrostatic film applied to the back side of
one or both substrates. Alternatively, an edge where the two substrates
join may be sealed, e.g., with a tape, so that reactants cannot reach the
back sides during processing. The dual substrate may then be wound into a
coil and coated such that both front surfaces are treated while the back
surfaces are not. Processing the substrate in this fashion may reduce the
waste of reactants and may increase the area of the substrate that can be
processed at one time. Optionally, other embodiments may use a
sacrificial backside that is removed after processing to reveal a
backside that is not processed. These systems are particularly suited for
a bath-type system wherein the substrate is passed through a solution
that exposes both sides of the substrate.

[0067] Referring now to FIG. 5, it should be understood that the
environment inside the oven may be different from the ambient atmosphere.
Although some embodiments may used an ambient air environment inside the
oven 180, other embodiments may use non-air atmospheres. By way of
example and non-limiting example, the atmosphere in the muffle 182 may be
comprised of ammonia or ammonia based material to prevent loss of ammonia
or similar material from the solution. The loss of material may create a
change in pH that changes the reaction dynamics. Other embodiments may
use other atmospheres that create an overpressure of the material that
may be volatile and escape from the solution during processing. The
material in the gas environment of muffle 182 is based on what type of
reaction is occurring and what materials may be vaporized or lost during
processing.

[0068] By way of example and not limitation, the muffle 182 may be
designed with openings sized to handle foils of wide widths. In one
nonlimiting example, the substrate 50 may be at least 1 meter in width.
In another embodiment, the substrate 50 may be at least 2 meters in
width. In another embodiment, the substrate 50 may be at least 3 meter in
width.

[0069] In one embodiment, the openings in muffle 182 are sized so as to
provide minimal clearance above the substrate to reduce the amount of gas
escaping. In one embodiment, the interior height of the muffle is less
than about 3 inches. In one embodiment, the interior height of the muffle
is less than about 2 inches. In one embodiment, the interior height of
the muffle is less than about 1 inch. In one embodiment, the interior
height of the muffle is less than about 0.5 inches. Although not limited
to the following, the ratio of the interior width to the interior height
at the narrow points in the chamber or muffle may be at least about 10:1.
Although not limited to the following, the ratio of the interior width to
the interior height at the narrow points in the chamber or muffle may be
greater than about 10:1. Optionally in other embodiments of the
invention, the ratio of the interior width to the interior height at the
narrow points in the chamber or muffle may be greater than about 14:1.
Although a muffle is used in this example, it should be understood that
other designs using a cover over a U cross-sectional shaped web guide may
also be sufficient to create the desired covered tunnel environment. In
one embodiment, the height of the head space above the substrate is
predetermined based on the processing gas and/or fluid used in that
particular zone or area of the processing system.

[0070] In some embodiments herein, the muffle 182 may be multi-zoned with
separate chambers in the muffle. These zones may be integrated into one
structure or they may be separated detached structures each defining at
least one zone. The zones may be separated from each other by a small
gap, or alternately all zones may structurally be connected to each
other, however they may be internally separated through use of seals or
spacers.

[0071] FIG. 5 also shows in phantom that a second muffle 190 may be used
around the inner muffler 182. The atmosphere in outer muffle 190 may be
the same as that in the inner muffle 182. Optionally, the muffle 190 has
an atmosphere different from that in the muffle 182. In one embodiment,
the muffle 190 includes an inert atmosphere such as but not limited to
nitrogen, argon, or the like. The muffle 190 may be the same length as
the muffle 182. Optionally, the muffle 190 may be longer than the inner
muffle 182 to prevent escape of gas into the outside environment. It
would instead escape into the outer muffle 190. Optionally, each muffle
may be inert gas zones near the inlet and outlet of each muffle to help
prevent escape of the interior processing gas. FIG. 5 also shows how
heater elements 192 and 194 may be located outside, above and/or below
the muffle.

[0072] Referring now to FIG. 6, yet another embodiment of the present
invention is shown wherein multiple spray and heating locations are
shown. In this embodiment, a spray section 200 is used to deposit the
solution, followed by an oven section 202 to heat the liquid. This system
may be followed by spray section 204, oven 206, spray section 208, and
oven 210. The spray and oven sections may be repeated as desired to
create the layer on the substrate 50 of the desired thickness. In this
embodiment, each spray and oven section creates about 25 to about 35
nanometer thickness of the junction partner. Other embodiments may use
deposition sections that create thicker or thinner layers. Some may also
use sections to deposit different materials or different components used
for the junction partner. Still other embodiments may use ovens that run
at different temperatures. Some may have heat in about 70 to about 90C.
Optionally, others may heat higher to about 40 to about 90C. Optionally,
others may heat higher to about 90 to about 130C. Optionally, others may
use lower temperatures of about 55 to about 75C. The ovens may be
arranged to go high heat to low heat. Optionally, they may go from low
heat to high heat. Others may use a heat profile with high heat in the
middle oven, but lower heat at the beginning or end ovens. This heating
may be followed up by wash and dry units 90 and 100. An oven 220 may be
included to further dry the substrate and/or prepare it for the next
layer of processing. Some embodiment may roll directly to the next
deposition section which may be a TCO sputtering or other deposition
device. The substrate 50 may also come directly from CIGS or other
absorber layer deposition and processing in a complete roll-to-roll
process. It should also be understood that in alternative embodiments,
there may be an alternative embodiment with a delayed processing, e.g.
not direct and not step repeat. In these alternative embodiments, there
may be non-continuous processing of the substrate.

[0073] Referring now to FIG. 7, a still further embodiment of the present
invention will now be described. This embodiment uses a frame 250 that is
raised and lowered over the substrate 50. In a step-repeat function, the
substrate 50 may be advanced to place an unprocessed portion below the
frame 250. The frame 250 is lowered to contact the substrate 50 or close
enough to prevent significant loss (more than 10%) of the fluid over the
substrate during processing. Again, any solution deposition may be used.
A variety of solution-based coating techniques may be used to apply the
liquid including but not limited to wet coating, spray coating, spin
coating, doctor blade coating, contact printing, top feed reverse
printing, bottom feed reverse printing, nozzle feed reverse printing,
gravure printing, microgravure printing, reverse microgravure printing,
comma direct printing, roller coating, slot die coating, meyerbar
coating, lip direct coating, dual lip direct coating, capillary coating,
ink jet printing, jet deposition, spray deposition, ultrasonic spray
deposition, and the like, as well as combinations of the above and/or
related technologies. The surface of the substrate 50 can be modified by
the addition of a wetting agent to the solution, such as glycerine. The
liquid may also be a dispersion or ink containing the aforementioned
materials. Depending on such surface tension, application of the liquid
onto the substrate may optionally be conducted upside down.

[0074] The oven 80 is heated during, before, or after deposition of fluid
into the frame 250. After processing and heating, the frame 250 is raised
and the substrate 50 is advanced to place a new, untreated section below
the frame 250. Again, the oven 80 may have an ammonia or other atmosphere
as described above. The frame 250 maybe filled multiple times over one
section of the substrate 50 to build up the desired amount of thickness.
Other embodiments may use a frame 250 that moves with the substrate to
allow for a moving process where the substrate is not complete stopped.
The frame 250 may be lowered down over an area of the substrate while it
is outside the oven 80.

[0075] Referring now to FIG. 8, yet another embodiment of the present
invention will now be described. This embodiment shows that instead of
using seals, frames or other elements to help contain a fluid over the
substrate 50, the edges 53 and 55 of a flexible substrate 50 may be
curved, curled, or angled upward. This defines a cupped or bowl-type
cross-sectional shape that allows fluid to be filled therebetween as
indicated by line 57 shown in phantom. The depth of the fluid between the
upwardly curled edges 53 and 55 may be filled to a level below the upper
edges, below the upper edges, and/or optionally over the upper edges. By
way of example and not limitation, the depth of fluid over the substrate
50 may be in range from about 0.1 mm to about 20 mm. Optionally, in
another embodiment, the depth of fluid over the substrate 50 may be in
range from about 0.5 mm to about 10 mm. In the present embodiment, a
fluid deposition assembly 259 may be used to form a covering of fluid
over the substrate 50. Optionally, the assembly 259 and any other of the
deposition systems such as but not limited to drip, spray, or other fluid
coating devices may be mounted to move in manner such as but noted
limited to that as indicated by arrows 257 to improve coverage of the
fluid deposition over substrate 50. Optionally, this may be achieved by
mechanical motion laterally and/or by angulation of deposition nozzle,
hose, or other deposition device/assembly.

[0076] It should be understood that the fluid may be deposited by any of a
variety of solution deposition techniques including, but not limited to,
wet coating, spray coating, spin coating, doctor blade coating, contact
printing, top feed reverse printing, bottom feed reverse printing, nozzle
feed reverse printing, gravure printing, microgravure printing, reverse
microgravure printing, comma direct printing, roller coating, slot die
coating, meyerbar coating, lip direct coating, dual lip direct coating,
capillary coating, ink jet printing, jet deposition, spray deposition,
ultrasonic spray deposition, and the like, as well as combinations of the
above and/or related technologies. FIG. 8 shows one embodiment wherein
the fluid is sprayed onto the substrate 50. The fluid may being deposited
may be at a temperature that is substantially the same as that of the
substrate 50. Optionally, in other embodiments, the fluid may be cooler
than the substrate 50 or hotter than the substrate 50. Some embodiments
may heat the fluid so that it is warmer than the ambient temperature.
Some embodiments may use an air knife to cool and/or clean the substrate
prior to deposition of the fluid.

[0077] FIG. 9 shows that in one embodiment, the substrate 50 with or
without curls 53 and 55 may be moved into a closely spaced muffle,
covered oven, or other structure to minimize the amount of open space
above the substrate 50. These embodiments reduce the amount of
evaporation of the fluid covering the substrate 50. In the current
embodiment, the muffle 260 is used to define the covered oven through
which the substrate 50 passes. The muffle 260 is shown to have curved
wall surfaces to maintain the curved configuration of the substrate 50.
Some embodiments may optionally have slots or grooves defined by guides
262 and 264 (shown in phantom).

[0078] FIG. 9 also shows that an optional external oven 270 may be used
around the muffle 260. This embodiment allows for convective heating to
be used outside the muffle 260 to heat the muffle 260, the substrate 50,
and the fluid over the substrate 50. The oven 270 may be filled with the
same atmosphere as that inside the muffle 260. Optionally, the muffle 260
may be filled with an inert gas such as but not limited to nitrogen,
argon, other inert gas, or other gas suitable for use with the atmosphere
in the muffle 260. The over 270 may be the same length as muffle 260,
shorter than muffle 260, or longer than muffle 260.

[0079] Referring now to FIG. 10, a cross-section of a guide is shown for
curling the substrate 50 to have the formed edges 53 and 55. This
cross-section shows that substrate 50 may be transformed from a
substantially planar configuration to one with a configuration sufficient
to hold fluid therebetween. Again, guides 280 and 282 may be provided to
help curl the substrate upward. The surface 281 may be a low friction
surface such as but not limited to Teflon® or similar material. The
surfaces of guides 280 and 282 may be similarly treated. Optionally, a
low friction surface 281 may comprise of a covering, tiles, plates, or
other overlayers that are placed on top of a surface that may have a
higher coefficient or friction. Some embodiments may have a low friction
surface along all portions of the substrate path wherein the backside of
the substrate contacts or slides against any portion of the processing
system.

[0080] FIG. 11A shows that the surface 284 of guide 280 may be a gradually
curving surface to transition the planar edge of the substrate to a
curved configuration. By way of example and not limitation, the length of
surface 284 as indicated by arrow 286 may be in the range from about 1
inch to about 10 inches. The greater length eases the transition from
planar configuration to curved configuration. Optionally, the transition
length may be in the range of about 2 to about 6 inches. Optionally, the
transition length may be a percentage based on the width of the web. In
one embodiment it may be between 10% to 120% of the width of the web.
Optionally, in another embodiment, the transition length is selected to
be between 25% to 75% of the width of the web or substrate. Optionally,
some embodiments also factor the height of the bent portion into the
amount of length desired for the transition. In one embodiment, the
length for transition is about 8× to 24× the height of the
desired bend. Optionally, the transition length is about 4× to
40× the height of the desired bend.

[0081] FIG. 11B shows yet another embodiment of the invention wherein the
guide 290 comprises of a plurality of discrete elements 292 that are
oriented to provide the same curving the substrate 50 to achieve the same
functionality as that of guide 280. By way of example and not limitation,
the discrete element 292 may be a roller, bearing, drum, or fixed roller.
Other rotatable, fixed, or other shaped discrete elements may be used to
guide the substrate 50. The guides may be any of a series of smooth
surfaces, angled surfaces, rounded surfaces, the like, or combinations of
the foregoing to achieved the desired configuration for substrate 50.
Again, any of the surfaces of the elements in FIGS. 11A and 11B may also
be coated or made of a low-friction material as described for surface
281.

[0082] Referring now to FIGS. 12A-12C, it should be understood that the
guides herein may be configured provide a variety of different
geometries. FIG. 12A shows that the substrate 50 may have angled but
substantially straight upward extending edge 293. FIG. 12B shows that the
substrate 50 may have a vertical but substantially straight upward
extending edge 295. FIG. 12C shows that the substrate 50 may have a
multi-bend upward extending edge 297. It should be understood that other
geometries of straight or curved sections may be combined in any order to
create the desired cross-sectional profile for the substrate 50. The
upward extending portion of the substrate 50 may be at any angle so long
as it is sufficient to contain or constrain the fluid over the substrate
50. It should be understood that the amount of upward bending portion (on
each side) may be described as a percentage of the cross-web width of the
substrate such as but not limited to between 1% to 7% of the web width,
with a minimum in this embodiment of at least 1 mm. Optionally, it may be
between 2% to 6% of the web width, with a minimum in this embodiment of
at least 2 mm. Optionally, it may be between 3% to 6% of the web width,
with a minimum in this embodiment of at least 3 mm.

[0083]FIG. 13 shows that the guides 280 and 282 may be positioned to
narrow the substrate 50 to achieve the curved configuration with the
curved edges 53 and 55. Guides 284 and 286 are similar to the guides 280
and 282, except that the configuration is reversed to gradually uncurl
the curved portions 53 and 55 and return the substrate 50 to a
substantially planar configuration. By way of example and not limitation,
it is desirable that the curling and uncurling occur in a manner that
does not cause substantially permanent deformation that causes warping or
damage to substantial portions of the substrate 50.

[0084]FIG. 13 also shows that when the edges of the substrate 50 is
configured to have curved portions 53 and 55, the width 283 of the
substrate 50 is less than the width 285 of the substrate 50 when planar.
The movement of the substrate 50 is in the direction as indicated by
arrow 294.

[0085] FIG. 14 shows that a cascade of one or more guides may be used to
gradually curve the substrate 50. In this embodiment of the invention,
the guides 280 and 282 are included. Additionally, a second set of guides
300 and 302 are included to further curl the substrate 50. This decreases
the width to that indicated by arrows 304. FIG. 14 also shows the
multiple guides 306, 308, 284, and 286 are used to uncurl, unbend, and/or
uncurve a selected portion of the substrate 50.

[0086] Referring now to FIG. 15, one embodiment of a deposition system 320
according to the present invention is shown. The deposition system 320
includes a deposition zone 322, a heated zone 324, a cleaning zone 326,
and a drying zone 328. A belt system 330 is used to transport the
substrate 50 through the heated zone 324. The deposition zone 322 may be
located in an unheated zone. Optionally, it may be included in the heated
zone 324.

[0087] FIG. 15 shows that in this embodiment an air knife or other gas
source 340 may be used to clean off the surface of the substrate 50. The
air knife or cleaning mechanism 340 may also be used to cool or
temperature regulate the substrate 50 before fluid is deposited onto the
substrate 50. This may be particularly useful as the belt system 330 may
carry some heat from the heated zone 324. Optionally, in other
embodiments, the belt system 330 may be sized such that the system 330 is
housed mainly in the heated zone 324 and does not extend into the
deposition zone 322 in manner that causes the substrate 50 to be heated
prior to deposition of the fluid thereon. By way of example, the
substrate 50 may be moved over a low-friction surface, free spanned in
the deposition zone 322, transported by a separate conveyor system, or
otherwise transported through the deposition zone 322. Some may have
sections of the processing system that are without any conveyor system
while other sections are conveyored. Some embodiments are entirely
without conveyors. Some systems may have the non-conveyored system with a
base have a pre-defined cross-section so as to curve or bend the
substrate upward when the substrate is laid on or pulled to conform to
the base.

[0088] In the present embodiment, the deposition assembly 350 used in the
deposition zone 322 may be a variety of solution deposition devices. It
should be understood that the fluid may be deposited by any of a variety
of solution deposition techniques including, but not limited to, wet
coating, spray coating, spin coating, doctor blade coating, contact
printing, top feed reverse printing, bottom feed reverse printing, nozzle
feed reverse printing, gravure printing, microgravure printing, reverse
microgravure printing, comma direct printing, roller coating, slot die
coating, meyerbar coating, lip direct coating, dual lip direct coating,
capillary coating, ink jet printing, jet deposition, spray deposition,
ultrasonic spray deposition, and the like, as well as combinations of the
above and/or related technologies. In one embodiment, a ultrasonic spray
system such as but not limited to the Prism Ultra-Coat system available
from Ultrasonic Systems, Inc. of Haverhill, Massachusetts may be used in
the deposition assembly 350. Some embodiments may use more than one fluid
deposition zone. They may use the same deposition technique or different
techniques. Some embodiments may combine more than one deposition
technique in the same deposition zone. It should also be understood that
the fluid may be deposited at a temperature that is substantially the
same as that of the substrate 50. Optionally, in other embodiments, the
fluid may be cooler than the substrate 50 or hotter than the substrate
50. Some embodiments may heat the fluid so that it is warmer than the
ambient temperature. Some embodiments may use an air knife to cool and/or
clean the substrate prior to deposition of the fluid.

[0089] By way of example and not limitation, it should be understood that
the heating zone 324 may use a variety of heating techniques. Some may
use convection heating, infrared (IR) heating, or electromagnetic
heating. Some embodiments may use chilled rollers or surfaces (not shown)
on the underside of the substrate 50 to keep a lower portion of the
substrate 50 cool while the upper portion is at a processing temperature.
As seen in FIG. 15, there may be one or more separate zones in the
heating zone 324. This allows for different temperature profiles during
processing. In one embodiment, the heating elements may be positioned to
heat all components in the heating zone to the same temperature. This
includes the cover over the substrate, a muffle, or other elements used
inside the heating enclosure. Again, heating may occur by convection
heating, infrared (IR) heating, and/or electromagnetic heating.

[0090] Referring still to FIG. 15, after the substrate 50 passes through
the heating zone 324, the cleaning zone 326 may use a combination of
washing, blowing, rinsing, suction, cooling, shaping, heating, and/or
other assemblies to post-treat the substrate 50 after the heating zone
324. In the present embodiment, a water sprayer 360 is used with an air
knife 362. A second water sprayer 364 is used with a second air knife
366. This combination is designed to remove any excess fluid that is not
reacted as the substrate 50 leaves the heating zone 324. The fluid and
waste liquid being washed off will be collected by one or more liquid
waste containers 370 and 372. The waste container 370 may be viewed as
the primary waste container as it will contain a more concentrated waste
fluid than the waste fluid filling the waste container 372. It should
also be understood that in some embodiments, the fluid from containers
370 or 372 may be reconditioned in reservoir 373 for use again in the
system. In one non-limiting example, used solution is cooled, and
replenished in a solution container 373 and redirected into the
deposition chamber.

[0091] There may be additional components such as filters on the return
line 325, filters (not shown) on the feed line 327, or filters in fluid
communication with reservoir 373 that may circulate the solution within
the solution container 22 for the purpose of particle elimination,
cooling, mixing etc. There may be a cooling loop with a cooling coil
within the solution container 373. A cooling liquid may be circulated
through the cooling coil to lower the temperature of the bath within the
solution container 373. The temperature of the solution within the
solution container 373 may be in the range of 5-40 C, preferably in the
15-20 C range. In effect the deposition section becomes a cold-wall
reactor where only the wall carrying the structure to be coated with CdS
is heated.

[0092] FIG. 15 also shows that in this embodiment of the invention, the
substrate 50 is dried after passing through the cleaning zone 326. Drying
zone 328 is positioned over the substrate 50 and will cure the material
on the substrate 50. In one embodiment, the drying zone 328 uses a
plurality of IR curing lamps to remove any residual moisture that may be
on the substrate. Optionally, in another embodiment of the invention,
heated gases may be circulated over the substrate 50 to remove any
residual moisture from the substrate 50. Some embodiment may circulate
heated inert gas such as but not limited to nitrogen. Optionally, some
embodiments may merely circulate heated ambient air that is drawn into
the drying zone 328.

[0093] It should also be understood that a variety of sensors may also be
installed along the path that the substrate 50 travels through the
deposition system 320. By way of nonlimiting example, this may include a
thickness sensor 380 positioned to detect the thickness of the coated
substrate. Optionally, other embodiments may use an optical sensor to
detect surface imperfection on the coated substrate 50. FIG. 15 also
shows that exhausts 390, 392, and 394 are positioned along the path of
the substrate 50 to draw off waste gases that may be created during
processing. Sensors may also be optionally present to optionally detect
chemical composition either on surface and/or through depth of coating.
Some embodiments may have optional sensor system to assess spatial
uniformity (not just aberrations but also standard uniformity).

[0094] It should also be understood that some embodiments may have
multiple heating zones 324. Some embodiments may have alternating zones
322 and 324. The zones may be combined various orders such as that shown
in FIG. 6. Cleaning zones 326 may also be included after one or more of
the heating zones 324.

[0095] Referring now to FIG. 16, yet another embodiment of the present
invention is now described. The deposition system 400 in FIG. 16 is
similar in some aspect to the system 320 shown in FIG. 15. By way of
example and not limitation, the heating zone 324 includes additional
convention chambers therein. The exhaust 394 is connected to its own
chamber 410. Deposition system 400 includes a substrate guide or contour
device 420 located upstream of the heating chamber. This substrate
contour device 420 will shape the edges of the substrate 50 to define an
area over the substrate 50 to hold fluid thereon. A second substrate
contour device 430 will uncurl the edges of the substrate 50 to return
the substrate 50 to a substantially planar configuration. One other area
of difference in the deposition system 400 involves the cleaning zone
326. The cleaning zone 326 in system 400 includes a suction element 440
for removing excess fluid from the substrate 50 after processing through
the heating zone 324. This suction element 440 provides for increased
control of fluid being removed from substrate 50 prior the washing and
blowing elements similar to that of system 320.

[0096] Optionally, it should be understood that any of the embodiments
herein may be equipped with thermally conductive coverplate(s) 351 which
may include a plurality of fins or other heat transfer improving shapes
or features to improve the heat transfer from the convection system to
the substrate 50. The plates 351 may be made of a thermally conductive
material such as but not limited to steel, aluminum, titanium, or the
like. Optionally, in-line heating elements 353 may be also be included
below and/or above the substrate to improve heat transfer to the
substrate. They may be integrated to be part of the coverplates 351 or
separate discrete elements. Some embodiment may also use free-spanning
substrate 50 that is move without the use of a conveyor belt.

[0097] FIG. 17 shows a still further embodiment wherein a bath type
deposition system 500 is used with moving seals 502 and 504. The moving
seals 502 and 504 may cover the side, top, and/or bottom surfaces of the
substrate 50 as seen more clearly in FIGS. 24-28. The path of the
substrate 50 through the system 500 may be lowered to create a bath
inside the system 500 without spillage downweb or upweb. Again, any
solution deposition technique may be used. A variety of solution-based
coating techniques may be used to apply the liquid including but not
limited to wet coating, spray coating, spin coating, doctor blade
coating, contact printing, top feed reverse printing, bottom feed reverse
printing, nozzle feed reverse printing, gravure printing, microgravure
printing, reverse microgravure printing, comma direct printing, roller
coating, slot die coating, meyerbar coating, lip direct coating, dual lip
direct coating, capillary coating, ink jet printing, jet deposition,
spray deposition, ultrasonic spray deposition, and the like, as well as
combinations of the above and/or related technologies. The surface of the
substrate 50 can be modified by the addition of a wetting agent to the
solution, such as glycerine. The liquid may also be a dispersion or ink
containing the aforementioned materials. Depending on such surface
tension, application of the liquid onto the substrate may optionally be
conducted upside down. Heating of the web may occur after the deposition
has occurred and/or at the same time. Optionally, the solution may itself
be heated to a temperature above that of the substrate. The seals which
may be rubber, silicone etc., may be continually fed against the web at a
speed that is substantially equal to the linear speed of the substrate.
In this case there would be no relative motion between the sealing
members and the substrate during processing.

[0098] Referring now to FIG. 18, this embodiment shows that the substrate
50 may be passed through a bath 550 of Group IIB-VIA-based solution as
shown. The rollers 552 are positioned so as to prevent contact the coated
surface 554 of the substrate 50. Alternatively, some embodiments may
allow the rollers 554 to contact the coated surface. FIG. 18 shows that
this embodiment may optionally include a stirrer 560 to keep fluid moving
around the surfaces of the container. FIG. 18 also shows that a reservoir
570 may be included to create fluid flow in the bath. Conduits 572 and
574 may be used to couple the bath 550 to the reservoir 570.

[0099] Referring now to FIG. 19, yet another embodiment of the present
invention will now be described. FIG. 19 shows a shaped container 580
that contains a bath 582 therein. There may be movable surfaces 584
and/or 586 (shown in phantom) along the sides of the shaped container 580
to allow for deposits on those surfaces to be cleaned. Optionally, some
embodiments may have normal wall surfaces, but the container 580 is
frequently cleaned to remove and deposits formed thereon. Some
embodiments may also be fitted with a reservoir similar to reservoir 570
to allow for constant fluid flow in the container 570 and more
specifically along the walls of container 570 to minimize deposits
thereon. Similar to FIG. 18, the rollers 588 may be configured not
contact the coated surface 552 of the substrate 50. The shaped container
also prevents fluid from escaping. Heating elements may be included in
the bath or outside the container 580 to heat the bath 582 therein to the
desired processing temperature. Some embodiments may have the same
temperature throughout the bath 582. Optionally, other embodiments may
have different heating zones that may include barriers 589 in the bath
that separate different fluid zones that may have different temperatures.
These embodiments may or may not use the substrate edge bending
techniques previously described herein.

[0100] FIG. 20 shows a still further embodiment wherein an additional
material 600 is coupled to the edges of the substrate 50. This allows for
the material 600 to define the curved portion that allows a bath to be
defined thereon. The material 600 may be a disposable material or
reusable material. This minimizes the risk that the curling may scratch
or damage the coating on the substrate 50. The material 600 may comprise
of a variety of materials such as but not limited to Teflon, polymer,
silicone, or other material. The material 600 may be coupled to the
substrate 50 by adhesives or by heating.

[0101] As seen in FIG. 21, the material 600 may be in the form a sheet
that covers the entire backside of the substrate 50 and extends beyond
the edges of the substrate 50. This may be particularly useful when the
substrate 50 is a plurality of pre-formed, discrete, or pre-cut rigid
substrates and the material 600 is a pliable material to allow for
curving to define a zone over the substrate for holding the fluid. The
material 600 may act as a carrier on which pre-formed, discrete, or
pre-cut substrates may be placed. The carrier may then carry these
pre-formed, discrete, or pre-cut substrates through the processing
station(s). In some embodiments, the edges of the material 600 may be
pre-shaped to have the upward bending configuration and not separate
curling apparatus is need to help transform the material 600 from a
planar configuration to one with upwardly pointing edges.

[0102] FIG. 22 shows that another embodiment of the invention may use the
substrate 50 with strips of material 602 and 604 instead of an entire
backside sheet of material 600. The material 602 and 604 may be similar
to that used for material 600. The material 602 and 604 may be
sufficiently flexible to allow the upward extending portion to be formed
and allow a bath to be contained therein. This edge material may
optionally be disposable so that the materials 602 and 604 may be handled
more aggressively to get the desired throughput or shape. The same may
also be said of material 600 in embodiments where it is designed to be
disposable.

[0103] Referring now to FIG. 23A, it should be understood that some
embodiments may use a separate layer 610 that is attached to the backside
of the substrate 50. This provides backside protection of the substrate
50, may also prevent unwanted formation of junction partner material on
the backside, to act as a thermal mass to cool the backside, or to
protect the backside during the curling or uncurling process. This
backside material may be permanently attached to the substrate 50 or it
may be a disposable material that is removed. Some embodiments may have
the material dissolve away during processing.

[0104] FIG. 23B shows that two substrates 50 and 51 may be joined
together. Coating or otherwise treating both sides of one substrate can
result in waste of valuable reactants or may lead to extra processing
steps such as removing unwanted coatings. To avoid such waste or
undesired processing, two substrates may be attached together
"back-to-back" to form a dual substrate having, in effect, two front
sides with the back sides protected against undesired treatment.
Optionally, the substrates are attached in a manner that allows them to
be separated from each other after processing. By way of example the
substrates may be attached with a low-strength adhesive or electrostatic
film applied to the back side of one or both substrates. Alternatively,
an edge where the two substrates join may be sealed, e.g., with a tape,
so that reactants cannot reach the back sides during processing. The dual
substrate 50 and 51 may then be introduced into the bath and coated such
that both front surfaces are treated while the back surfaces are not.
Processing the substrate in this fashion may reduce the waste of
reactants and may increase the area of the substrate that can be
processed at one time. The substrates may be joined directly together or
may have an adhesive layer 612 therebetween.

[0105] FIGS. 24 through 28 show some of the various types of edge seals
that may be used with the substrate 50 or with substrate 50 and a
disposable edge material to allow for a bath to be formed over the
substrate 50. FIG. 24 shows that seal material 620 may be slidably or
fixably attached to an upper surface 622 of the edge of the substrate 50.
FIG. 25 shows that seal material 624 may be slidably or fixably attached
to a side surface 626 of the edge of the substrate 50.

[0106] FIG. 26 shows that shaped seals 630 formed against a side surface
626 and/or a bottom surface 632 of the substrate 50. The seals 630 may be
slidably or fixably attached to the substrate 50. FIG. 27 shows that a
shaped seal 640 may be formed against a side surface 626 and/or a top
surface 622 of the substrate 50. The seals 640 may be slidably or fixably
attached to the substrate 50. FIG. 28 shows that a shaped seal 650 may be
formed against a side surface 626, and/or a top surface 622, and/or a
bottom surface 632 of the substrate 50. The seals 640 may be slidably or
fixably attached to the various surfaces of substrate 50. Optionally, the
surfaces of shaped seal 650 engaging the surfaces of substrate 50 may be
angled and not necessary parallel to the surfaces against which they
engage. This may created a pinched contact if a tighter engagement is
desired.

[0107] Referring now to FIG. 29, yet another embodiment of the present
invention will now be described. FIG. 29 shows a top-down view of the
substrate 50 as it is being processed for formation of the junction
partner layer. This embodiment has a single fluid deposition source 700
that directs fluid onto the substrate 50. The source 700 may be oriented
to direct fluid downstream. This may be as a result of a slight angle of
the deposition system as seen in FIG. 3 and may help to prevent flow of
fluid upstream to un-contained areas where fluid may flow off the sides
of the substrate 50. The fluid deposition source 700 may also be designed
to have a reciprocating feature wherein the direction of the deposition
will move through a series of angles 702 to more evenly distribute fluid
over the substrate 50.

[0108] FIG. 29 also shows that one or more rotational stirring elements
710 and 712 may also be included in the present invention. The stirring
elements 710 and 712 may be the same or different size. They may be
positioned to create gas or air flow over the bath of fluid covering
substrate 50. This may be helpful in creating convection or flow to more
evenly distribute heat uniformly over the substrate 50. Optionally, the
stirring elements 710 and 712 may be fully in or at least partially
stirring the fluid over the substrate 50. They may be configured to
rotate in the same or different directions. Other, non-rotation devices
may also be used to create liquid flow or gas flow.

[0109] FIG. 30 shows a still further embodiment wherein there is more than
one fluid deposition assembly 720 and 722 which are positioned at
locations along the length and/or width of substrate 50. This may achieve
a desired even distribution of fluid over the substrate 50. Some
embodiments may have two or more fluid depositions assemblies. One or
more the fluid deposition assembly 720 and 722 may be movable across
different angles 702, similar to that as shown in the embodiment of FIG.
30. For any of the embodiments herein, a static or active mixer may be
used upstream of the deposition assemblies to mix the fluids together
prior to deposition onto substrate 50.

[0110] Referring now to FIG. 31, yet another aspect of the present
invention will now be described. FIG. 31 shows a conveyor belt 730 with
vacuum holes 732 therein to allow for suction of a substrate 50 thereon.
This is useful to facilitate transport of the substrate 50 without
scratching the underside. The vacuum holes 732 in the belt are suctioned
by way of a vacuum source 734. The conveyor belt 730 may be sized to be
the same as or almost the same width as the substrate 50. Optionally, it
may be wider than the substrate 50. Optionally, belts 730 that are less
wide may also be used. The thinner belts 730 may be used to suction down
the substrate 50 at various strategic locations. Some embodiments may
also use shaped conveyors which provide the desired contour at the edges
of the substrate 50. Such shaped conveyors may have a lip 733 (shown in
phantom) that may help to maintain the contour of the substrate 50 being
transported by the conveyor. In some embodiments, the conveyor may be
made of a thermally conductive material such as but not limited to a
metal belt of titanium, stainless steel or the like. Optionally, the
conveyor may be made of a polymer or thermally insulating material.

[0111] Optionally as seen in FIG. 32A, on some very low surface transport
surfaces, instead of using vacuum holes on the belts, the vacuum holes
732 may optionally be formed onto the low-friction surface 738. In one
embodiment, the low-friction surface may be a Teflon® surface.
Optionally, it may a surface with a static coefficient of friction
between about 0.12 to about 0.20. Optionally, it may a surface with a
static coefficient of friction between about 0.10 to about 0.30. This may
allow the substrate to be held flat as it is pulled across the transport
surface. This may be of particular use since the substrate 50 may be
somewhat non-flat after processing.

[0112] Optionally as seen in FIG. 32B, on some very low surface transport
surfaces, instead of using vacuum holes on the belts, the vacuum channels
733 may optionally be formed onto the low-friction surface 738. In one
embodiment, the low-friction surface may be a Teflon® surface.
Optionally, it may a surface with a static coefficient of friction
between about 0.12 to about 0.20. Optionally, it may a surface with a
static coefficient of friction between about 0.10 to about 0.30. This may
allow the substrate to be held flat as it is pulled across the transport
surface. This may be of particular use since the substrate 50 may be
somewhat non-flat after processing. The channels 733 may be oriented
cross-web as shown in FIG. 32B, and/or optionally, oriented down web (or
have both). The channels 733 can be spaced or sized so that the top
surface of the web or foil remains sufficiently flat so as to be
submerged or covered by the processing fluid. The channels 733 may be
full length cross-web so as to keep the entire web width pulled flat
against the low-friction surface of the bed. Although the channels 733
and/or the holes 732 are shown in use with a bed that has curved edges,
other shapes such as but not limited to flat, convex, concave, or the
like are not excluded. If the holes are not spaced correctly, the
channels are made across, so all the foil sees the same gap. The suction
keeps the foil flat to keep the foil flat. In some embodiments, the bed
may be coated with Teflon or other low friction material.

[0113] Some embodiment may have a belt formed of discrete individual
elements or slabs 735 with or without the lip 733 to maintain the curved
shape. One nonlimiting example is seen in FIG. 32C. Each of the elements
735 may be equipped to include force holding elements such as but not
limited to vacuum and/or magnetic force to pull the substrate or web
against the element 735. Some embodiments may also include heating
elements inside or on the surface of the elements 735 to provide heat to
the web. The elements 735 can include any of features shown in FIGS.
32A-32B such as channels, holes, curved perimeters, etc.

[0114] Referring now to FIG. 33, a still further aspect of the present
invention will now be described. This shows that a substrate 50 may be
taken along a path that dips to allow for a bath to be created at
recessed area to minimize the loss of process fluid either upstream or
downstream. This dip 740 in the path may be achieved through the use of
rollers or other web guiding devices to direct the substrate 50 to a
lower pathway. The substrate 50 may remain at this lower level and the
rise upward vertically or at an angle to rise out of the lower path.

[0115] Mixing

[0116] Referring to FIGS. 34-39, static and/or active mixers can be used
to create laminar and/or turbulent flow in the process fluid as it lies
in situ over the substrate being processed.

[0117] Referring to FIG. 34, mechanically stirring of the fluid can be
achieved in one embodiment by rotational stirrers, with all the stirrers
in line or staggered to mix entire web down web. With circular elements,
the waves are different, depending on rpm rotation speed of the stirrer.
It should be understood that in other embodiments a stirring arm using
linear motion instead of circular motion can be used. Other types of
mechanical motion are not excluded for use in stirring the liquid.

[0118] Some embodiments may use stirring by air, standing waves, and/or
other methods for stirring.

[0119] By way of nonlimiting example, one method of stirring the
processing solution involves stirring using process gas flow. In this
embodiment, there is gas flow due to pressure differential in the head
space above the processing solution. In one embodiment, gas flow with
crossweb baffles creates high velocity regions over pre-defined areas of
the foil. The narrowing created by the baffles creates high velocity
regions in the low-gap areas over the processing solution. Although not
limited to the following, the ratio of the interior width to the interior
height at the narrow points in head space may be at least about 10:1.
Although not limited to the following, the ratio of the interior width to
the interior height at the narrow points in the head space may be greater
than about 15:1. Optionally in other embodiments of the invention, the
ratio of the interior width to the interior height at the narrow points
in the head space may be greater than about 20:1. Optionally in other
embodiments of the invention, the ratio of the interior width to the
interior height at the narrow points in the head space may be greater
than about 30:1. Optionally in other embodiments of the invention, the
ratio of the interior width to the interior height at the narrow points
in the head space may be greater than about 40:1. Optionally in other
embodiments of the invention, the ratio of the interior width to the
interior height at the narrow points in the head space may be greater
than about 50:1. Optionally in other embodiments of the invention, the
ratio of the interior width to the interior height at the narrow points
in the head space may be greater than about 75:1. Optionally in other
embodiments of the invention, the ratio of the interior width to the
interior height at the narrow points in the head space may be greater
than about 100:1. In some embodiments, the head space may be in the range
of 0.5-5 mm, optionally in the range of 1-3 mm, whereas the width of the
substrate employed may be in the range of 0.3-2 m. For a 1 mm gap and 1 m
wide substrate, the ratio of the wetted workpiece total front surface
area to the wetted sealing member total area is about 200 cm/0.2 cm=1000.

[0120] Stirring by having baffles; a high velocity region in the process
zone created by the baffle.

[0121] Stirring all over the crossweb width helps uniformity. The baffles
creates mixing in the solution. In one embodiment, there are many baffles
down the web. This keep as much process gas such as but not limited to
ammonia. So, the baffles create more obstructions before it reaches
exhaust, in addition to creating areas of high velocity.

[0122] Exhaust pulls the liquid off. Confined headspace opening into a big
volume. A pressure reader can be used.

[0123] The baffles in one embodiment may be staggered cross-web. It could
be evenly located across web. Going all the way across is to mitigate
loss of ammonia.

[0124] In some embodiment, edges not getting good coverage by processing
solution, so baffling or other mixing devices extending to the edges or
all the way across the web can be used. This gives the ammonia longer
residence in the head space before it is exhausted. In one non limiting
example, the gap between top of fluid and baffle is about 5 mm. In one
embodiment, the baffles are on the chamber doors associated with each
chamber.

[0125] Other embodiments may recirculate the processing gas, an inert gas,
or other gas for mixing of liquid solution.

[0126] Other embodiments use sonic vibration for mixing.

[0127] In one embodiment, vibration of any frequency can be actuated to
cause mixing of fluid on the substrate. This can be by vibration of the
bed, vibration of the web, contact of vibrations with the solution,
contact of vibrations with the bed, contact of vibrations with the
process gas above the processing solution, contact of vibrations with the
process gas, etc.

[0128] Some embodiments tune frequency to get wave patterns across
solution over the web. This can be designed to create wave only down web
or only crossweb.

[0129] One embodiment for stirring uses the sideways flat arm to create
fluid flow. Optionally, another embodiment uses anything that does not
contact the web or liquid on the web to create flow or mixing. If it is
non contact, vibration may be one of the candidates and can be used alone
or with other contact type methods such as mechanical stirring or any of
the other embodiments herein.

[0130] Optionally, one embodiment sets up standing waves in the processing
solution on the substrate. If one has standing waves, the standing waves
should be changed, else there is more solution at one spot than the
other. Thus the embodiments herein will change the standing wave to move
to create better uniformity. This changes the peak of the wave.

[0131] The stirring can be desirable to improve uniformity. The path of
the fluid moves more at the areas of the baffles over the substrate which
impede process gas flow. Slots may be placed in the baffles, the baffles
can extend full length or only part length. Uniformity assistance is
desirable, particularly in wide web where there is wide web.

[0132] Fluid velocity is desirable. Laminar flow and/or turbulent flow can
be created. With laminar, it is more difficult to achieve mixing but is
not excluded. Some embodiments may include not mixing the bottom.
Optionally, some use turbulent flow or other flow that causes mixing that
extends directly to the surface of the substrate. Stirring can disrupt
stripes from laminar flow in some embodiments.

[0133] Stirring replenishes chemistry at the surface of the substrate that
is being processed. In most embodiments, it is desirable to have
chemistry that is refreshed. Possible that the solution is already used,
since reactants are used. Some embodiments may use deeper baths or
heights of liquid (more than 2 mm on a 1 m wide web) to have more
processing liquid over the substrate. Optionally, some may have more than
3 mm on a 1 meter wide web.

[0134] Optionally, as seen in FIG. 37, some could have a second location
700 for injecting more process solution into the web. Optionally, some
could be in different chambers or all the same chamber for multiple
injection point. This can be useful if the process solution is being
used/depleted. Optionally, some embodiments may want to clean the web
using a first solution before adding the processing solution at the
second location 701. The first solution may be removed in one embodiment
at a washing station before process solution is used at location 701.
Optionally, some do not use a washing station. Optionally, some use the
processing solution (un-heated or heated to a level that does not cause
reaction or grow of CdS) to clean the web before heating and/or before
the second location 701 which introduces more processing solution. Thus
in the example for forming CdS, the cleaning solution may be the cadmium
solution, the complexing agent (ammonium hydroxide), or thiourea. Some
may be single or double combinations of the components. Some may use all
three components as the cleaning solution, except at a temperature below
that used for processing.

[0135] Fresh ammonia gas or processing gas:

[0136] In one nonlimiting example, this could be used as a method of
stirring: gas stirring by introducing ammonia. This may involve
recirculating gas in the head space that is well sealed or leak free over
the heating zones along the process path.

[0137] Thus, some embodiments add fresh processing gas, which in the case
of CdS may be ammonia. This embodiment adds new gas to keep the ammonia
saturated along with fresh ammonia or processing solution that may be
added to the liquid. This keeps the ammonia atmosphere saturated to keep
fresh ammonia solution from degrading as it is being introduced. The
ammonia is a complexing solution and a change in concentration can cause
too much precipitation of solid in at an undesirable rate. Some
embodiments simultaneous introduce new process gas and new process
solution.

[0138] Heating:

[0139] In some embodiments, the foil or substrate is heated by one more
combination of heating sources such as but not limited to heating the
bed, which heats the foil, and that causes evaporation. There is another
heater which heats the air or gas, which may be above the cover plate of
the chamber or inside the chamber. In one embodiment, the temperature set
point is higher than the heated bed.

[0140] Optionally, some embodiments may have "stalactites" or downward
protruding condensation structures 900 in the chamber as seen in FIG. 47.
In one embodiment, these structures are staggered cross web and/or
downweb: one row, another row that is offset by 50 percent or some other
ratio. Optionally, the structures 900 may be a fin or vane the runs cross
web or at angles to create sharp points or thin edges along which
condensation may form. This allows for process gas that is condensed to
return to the processing solution in the solution over the substrate.
This allows the gas to return into the liquid in controlled manner and at
a controlled location. It can also create stirring as the condensation
droplets create stirring. Some embodiments merely keep the stalactites
heated to a lower setpoint relative to the temperature of the vapor.
Although active cooling is not excluded, merely keeping the temperature
5% cooler than the surround gas is sufficient in on embodiment to create
condensation. Optionally, some embodiments keep the temperature 10%
cooler than the surround gas. Optionally, some embodiments keep the
temperature 15% cooler than the surround gas. Optionally, some
embodiments keep the temperature 20% cooler than the surround gas.
Optionally, some embodiments keep the temperature 25% cooler than the
surround gas. Optionally, some embodiments keep the temperature 30%
cooler than the surround gas. In one embodiment, the condensation is
sufficient to keep active reagents reintroduced into the liquid.

[0141] In one embodiment, it is desirable to control the amount of ammonia
or process gas in the head space. Optionally, this amount is equivalent
to the vapor pressure of ammonia at the processing temperature (or
concentration). The steady state can be the point where no transfer in
either direction is occurring (evaporation from solution to vapor or
transfer of vapor into the solution). This can be maintained for preset
times such as but not limited to 4-5 minutes in the zones that are
heated.

[0142] Ammonia evaporation will occur less where it is less heated or
where there is sufficient ammonia in the atmosphere to minimize
evaporation.

[0143] Baffle plate can be used to create circulation. This can be in the
atmosphere over the fluid (such as in the muffle) and/or some embodiments
may use the baffle plates in contact with the fluid over the substrate.

[0144] Some embodiments may use different temperature zone in the oven
(ramp is from room temperature to hold at 83C, optionally about 90C,
optionally about 100C, optionally about 110C, optionally about 120C).
Crossweb zones and down web zones can be used. Some embodiment may have
systems that are slow ramping.

[0145] Some embodiments keeping the solution cold to clean the web prior
to heating of the web or substrate at the processing bed.

[0146] In some embodiments, both solutions are in there in the cleaning
Optionally, some embodiments just use dilute ammonia hydroxide.

[0147] This embodiment uses both (inline mixer) which leads to better
mixing. Optionally, some clean with one solution, get rid of it, and then
introduce both solutions for processing.

[0148] Seals for Vapor Containment

[0149] Referring now to FIGS. 40-44, containment can be used along the
perimeter of the sides of the substrate so that the loss of ammonia is
minimized. At the edges of the substrate, edge seals can be used for
vapor control to prevent loss out the side of the zone.

[0150] FIG. 40 shows a cross-sectional view showing the width of the web
and that lips 800 can extend into the fluid so that a seal is created by
the contact with the liquid (liquid level is indicated by the phantom
line). Seals by lips 800 into the fluid do not contact the web, although
in some embodiments, such contact is not excluded so long as it does not
damage the web or any films formed or forming on the web. The atmosphere
802 is sealed from escaping out the sides. Some embodiments may have
specific locations where gas is exhausted out. The lips 800 may extend
downweb to extend the sealed zone along the entire processing zone, only
along heated zones, or in other select areas.

[0151] Referring now to FIG. 41, another variation of the embodiment of
FIG. 40 shows that seals 804 may be used that seal against the edge of
the substrate 50 and extend into atmosphere and close to, but not
directly contacting the fluid over the substrate 50.

[0152] Referring now to FIG. 42, another variation the seals 805 sized to
extend into the fluid over the substrate 50. This allows for the seal
against the edge of the substrate at location 806 to be an optional seal.
In this manner, there can be variations in the contact without causing a
significant loss of seal. In this embodiment, there are at least three
different vapor zones 807, 808, and 809 over the fluid on substrate 50.
In one embodiment, the zones 807 and 809 are sized to be significantly
smaller than that of the main zone 808. By way of non-limiting example,
the surface areas in zones 807 and 809 are together less than 10% of the
total area of all three zones. Optionally, the surface areas in zones 807
and 809 are together less than 5% of the total area of all three zones.
Optionally, the surface areas in zones 807 and 809 are together less than
2% of the total area of all three zones. Optionally, the surface areas in
zones 807 and 809 are together less than 1% of the total area of all
three zones. The material for seals can be one that does not interact
with the chemistries in the fluid. Some polymeric or other materials may
be coated with Teflon in one embodiment. In one embodiment, the seals 805
extend downweb along the length of the process zone. Optionally, the
multiple seals 805 are used on each side to extend downweb along the
length of the process zone. In some embodiments, only select portions of
the process zone (such as those with areas of high evaporation) have the
seals.

[0153] The seals 805 may be multi-component, such as that described below.
Optionally, the seals 805 are fixed while the web or substrate 50 slides
against it. Optionally, some embodiments may have moving seals 805 that
move at the same rate or other rate relative to the substrate 50. In some
embodiments, the seals 805 create a seal at a first location (at the edge
of the foil) and create a second seal at a second location (at the tip
that extends into the fluid). Optionally, some embodiments only seal at
the second location (in the fluid). Optionally, some seals in the second
location and only partially at the first location, due to variance in the
edge of foil.

[0154] Referring now to FIG. 43, some embodiments use seals up against the
edge of the foil (side or top contact). This can be a moving seal that
moves at the pace of the substrate. The end effector 810 can be rubber,
silicone, etc., and may be continually fed against the first flexible
substrate along the two long edges of the two workpieces or substrates,
at a speed that is substantially equal to the linear speed of the
substrate. In this case there would be no relative motion between the
sealing members 810 and the substrate during processing. Optionally, the
member 810 extends fully across the web in on continuous piece and it not
just discrete pieces only at the ends.

[0155] Optionally, it is a seal with the substrate slides against the seal
material 810. Some embodiments may include an accordion structure,
compliant section, or spring structure 812 that allows the seal 810 to be
pressed against the edge to maintain the integrity of the seal even in
location where the substrate may want to disengage. Some seals 810 may be
a plurality of discrete elements so each section can press down against
the substrate independently so that the contact is not lost.

[0156] FIG. 44 shows another embodiment wherein the spring for compliance
uses an accordion edge seal for a side contact seal 820. Rubber accordion
edge seal 822 is used to laterally push the seal 820 against the side
edge of the web or substrate. There is a compliant part and an actual end
effector 820. By way of example and not limitation, the end effector 820
can be a nylon based material or any sufficient to be durable and seal
against the substrate.

[0157] This can be to reduce the amount of solution and also provide a
controlled process by prevent leaks from the side of the substrate. These
seals can extend along the entire length of the process zones or only in
select areas.

[0158] Referring now to FIG. 45, yet another embodiment of the present
invention is shown wherein rollers 830 (which rotate or are fixed) can be
used to create cross-web sealing of the atmosphere over the process
zones. In one embodiment, the rollers 830 can directly contact the
substrate, sometimes used to create a vapor seal while also flattening
the substrate, although rollers 830 not in direct contact with the
substrate 50 are not excluded. Optionally, some such as roller 832 is
only in contact with the fluid, but not directly with the substrate 50.
The roller in some embodiments extends beyond the cross-web width of the
substrate. Optionally, some are less than the cross-web width such as but
not limited to about 95%, 90% or more of the width.

[0159] Fluid Flow

[0160] Referring now to FIG. 46, it is desirable in some embodiments that
there is flow of the fluid relative to the substrate, with relative flow
of the fluid away from the deposition site. Without such flow or if the
flow is at the same speed as the movement of the substrate (i.e. no
relative motion between the two), then the chemistry in the fluid can be
depleted without being refreshed by flow of new fluid. It can also create
non-uniformities due to lack of mixing of the fluid over the substrate
50. In some embodiments, only the bed portion or processing zone is
angled. Some embodiments may angle the entire apparatus. Some may have
portions at one angle and different portions at a different angle.

[0161] In one embodiment, the primary method for achieving the relative
flow is through the tilting or angling of the bed or platform supporting
the substrate. This creates an angle that through gravity, will cause a
relative flow over the substrate. In one embodiment, the bed is angled to
drop 1 inch every 15 yards. Optionally, the angle creates a drop of 1
inch every 12 yards. Optionally, the angle creates a drop of 1 inch every
10 yards. Optionally, the angle creates a drop of 1 inch every 7 yards.
Optionally, the angle creates a drop of 1 inch every 5 yards. Optionally,
the angle is between one that creates a drop of 1 inch every 15 yards to
a drop of inch 1 every 5 yards.

[0162] Drying

[0163] Drying is typically at the end of the process: after liquid is
removed, the web is heated. This gets the web hot enough to dry surface
water, but also absorbed water, such as residual water. Temperature is at
least 100C in one embodiment. The web is heated to 100C. Optionally,
temperature is at least 120C in one embodiment. The web is heated to
120C. Heater is above and below to heat the web.

[0164] In one embodiment, IR curing lamp or IR lamps+heat the air more
effectively dries the web. Getting the heat into the web can also involve
using air that is dried. In some embodiment, it is better to have dried
air (not ambient) or ambient controlled to always have a specific
humidity or to be in a controlled atmosphere. In this manner, process
variability is reduced based on the day to day changes in humidity.

[0165] Head Space

[0166] It should be understood that in some embodiments as seen in FIG. 9,
it is desirable that a low head space is kept above the web or foil. In
one embodiment, the interior head space (distance from surface of
processing solution to surface of the top of the chamber) is less than
about 3 inches. In one embodiment, the interior height of the head space
is less than about 2 inches. In one embodiment, the interior height of
the head space is less than about 1 inch. In one embodiment, the interior
height of the head space is less than about 0.5 inches. Although not
limited to the following, the ratio of the interior width to the interior
height at the narrow points in the chamber or head space may be at least
about 10:1. Although not limited to the following, the ratio of the
interior width to the interior height at the narrow points in the chamber
or head space may be greater than about 10:1. Optionally in other
embodiments of the invention, the ratio of the interior width to the
interior height at the narrow points in the chamber or head space may be
greater than about 14:1. Optionally in other embodiments of the
invention, the ratio of the interior width to the interior height at the
narrow points in the chamber or head space may be greater than about
20:1. Some may be greater than the ratios above but less than 1000:1.
Although a muffle is used in this example, it should be understood that
other designs using a cover over a U cross-sectional shaped web guide may
also be sufficient to create the desired covered tunnel environment. In
one embodiment, the height of the head space above the substrate is
predetermined based on the processing gas and/or fluid used in that
particular zone or area of the processing system.

[0167] The overall control of the processing atmosphere such as but not
limited to the ammonia atmosphere is desirable to control the
concentration of active agents in the processing solution. Some advantage
of sealing the head space (in addition to or in place of low head space)
above the solution, is that then all of the vapor trying to escape is
trapped. This enables better control as there is less variability due to
escaping material into the vapor. Then the system can run with less
solution, since there is tighter control of the solution. There is less
need to introduce more fresh solution due to loss from evaporating
solution into the uncontrolled atmosphere above the foil.

[0168] In one embodiment, it is more keeping the head space saturated
above the foil, in addition or in place of a low head space. The glass
doors or chambers are to be gas tight, leak proof seals. Doors are
provided for easy access, maintenance, but some embodiments may not have
doors.

[0169] Optionally, others use rollers to curl the sides of the substrate.
By way of non limiting example, it could be along the whole length, key
areas, or just at the beginning when the shape. This embodiment
plastically deforms the foil. Some do not.

[0170] While the invention has been described and illustrated with
reference to certain particular embodiments thereof, those skilled in the
art will appreciate that various adaptations, changes, modifications,
substitutions, deletions, or additions of procedures and protocols may be
made without departing from the spirit and scope of the invention. For
example, with any of the above embodiments, the present invention may be
adapted for use with superstrate or substrate designs. The tool designs
of this invention may be used for continuous, in-line processing of
substrates which may be in the form of a web or in the form of large
sheets such as glass sheets. The substrate may be a continuous web or
sheet of a metal or an insulator comprising a precursor layer that has
been reacted to form a compound film absorber layer. The present
invention is not limited to deposition of junction partner material. By
way of nonlimiting example, it may also be used to deposit precursor
materials for photovoltaic absorber layers. Optionally, it may be used to
deposit materials for use as or precursor materials that form:
anti-reflective coatings on cells or modules, moisture barriers on such
modules or devices, encapsulant materials, adhesive materials, conductive
materials, insulating materials, and/or semiconducting material. The
inclination angle of the curved edges may be in the range of 5-15
degrees. The amount of bend at the two long edges of the flexible
substrate may be in the range of 2-10 mm, preferably in the range of 3-6
mm

[0171] Various buffer layers with various chemical compositions have been
evaluated in solar cell structures. CdS, ZnS, Zn--S--OH, Zn--S--O--OH,
ZnO, Zn--Mg--O, Cd--Zn--S, ZnSe, In--Se, In--Ga--Se, In--S, In--Ga--S,
In--O--OH, In--S--O, In--S--OH, etc. are some of the buffer layer
materials that have been reported in the literature. Buffer layers for
Group IBIIIAVIA devices such as CIGS(S) solar cells may be 5-200 nm
thick.

[0172] In one embodiment, the aqueous CdS deposition bath may be formed by
mixing in water 1-50 ml of 1M cadmium salt solution, such as Cd-chloride,
Cd-sulfate, Cd-acetate, or the like, 1-50 ml of 14.53 M ammonium
hydroxide solution as complexing agent, and 1-50 ml of 1M thiourea as S
solution. Another complexing agent solution such as 0.5M Triethanolamine
(TEA) may also be added in an amount that is in the range of 1-20 ml,
although some embodiments do not use more than one complexing agent.
Optionally, the bath may contain (by volume) 5-15% cadmium solution,
5-15% complexing agent (ammonium hydroxide), 5-15% S solution (thiourea)
and optionally 5-10% of the additional complexing agent solution (TEA),
the balance being the solvent, i.e. water. Some embodiments may use more
thiourea in the range of about 15-50%.

[0173] Homogeneous reactions within such solutions initiate once the
temperature is raised, for example, to over 50 C. A bath may be stable
for over 5 hours at 20C., whereas large particles may form within minutes
in a bath that is heated up to 80C. The above mentioned CdS bath acts in
a similar fashion. Since the solution is mostly kept at low temperature
for the method of the present invention, it is possible to mix all the
ingredients of the solution. In prior art techniques it is customary to
mix the Cd source and the complexing agent in the solvent, then heat up
the solution to 50C or higher, and then add the S source, at which time
reaction and CdS formation starts.

[0174] For any of the embodiment herein, the substrate may be an elongate
material suitable for use in a continuous, roll-to-roll process.
Optionally, there may be a carrier on which discrete or pre-cut
substrates comprising the precursor layers may be placed. The carrier may
then carry these discrete or pre-cut substrates through the processing
station(s). The carrier may be the same or a different material from the
discrete, pre-cut, or individual substrate. The carrier may be
sufficiently pliable to be shaped to create the zone to hold sufficient
fluid on the carrier to submerge the discrete or pre-cut substrates in
processing fluid. In any of these embodiments, the substrate may be moved
continuously at the same or different rate, or optionally in sequential
stop and go steps.

[0175] The heating steps and cooling steps may be repeated either for
depositing thicker CdS on the same surface or for depositing CdS on
surfaces of new structures introduced into the deposition section in a
cyclic or continuous manner. Optionally, some embodiments may use
continuous recycling of the solution between the solution container
collecting used solution and the deposition section, although
intermittent flow of the solution between the deposition section and the
solution container may also be utilized. Once the solution is in the
recirculating solution container it may be analyzed for its composition
and ingredients that may be reduced due to reactions may be added to the
solution. Such ingredients include but are not limited to water, ammonia,
Cd salt, S source, complexing agent etc. By controlling the solution
composition this way, the same solution may be used for coating a large
number of structures with CdS without replacing the base solution. This
reduces waste and thus cost of the process. The base solution may be
occasionally replaced with a fresh one if its impurity content increases
to a level that may affect the quality of the deposited CdS film. Removal
of particles from the solution may be achieved through filtration using
various approaches including centrifuging the solution. The CdS particles
thus removed may be re-cycled later to form a Cd source for the process.

[0176] With regards to the type of various junction partner suitable for
use with the present invention, various chemical compositions have been
evaluated in solar cell structures. CdS, ZnS, Zn--S--OH, Zn--S--O--OH,
ZnO, Zn--Mg--O, Cd--Zn--S, ZnSe, In--Se, In--Ga--Se, In--S, In--Ga--S,
In--O--OH, In--S--O, In--S--OH, etc. are some non-limiting examples of
possible materials. Such layer maybe in the thickness range of about
5-200 nm thick and may be deposited by various techniques such as
evaporation, sputtering, atomic layer deposition (ALD), electrodeposition
and chemical bath deposition (CBD), etc

[0177] In one example, a suitable solution for growing a cadmium sulfide
(CdS) layer employs a chemical bath comprising cadmium (Cd) species (from
a Cd salt source such as Cd-chloride, Cd-sulfate, Cd-acetate, etc.),
sulfur (S) species (from a S source such as thiourea) and a complexing
agent (such as ammonia, triethanolamine (TEA), diethanolamine (DEA),
ethlene diamine tetra-acetic acid (EDTA), etc) that regulates the
reaction rate between the Cd and S species. In one example, the
deposition bath may be formed by mixing in water 1-50 ml of 1 M cadmium
salt solution, such as Cd-chloride, Cd-sulfate, Cd-acetate, or the like,
1-50 ml of 14.53 M ammonium hydroxide solution as complexing agent, and
1-50 ml of 1M thiourea as S solution. Another complexing agent solution
such as 0.5M Triethanolamine (TEA) may also be added in an amount that is
in the range of 1-20 ml. A typical bath may contain (by volume) 5-15%
cadmium solution, 5-15% complexing agent (ammonium hydroxide), 5-15% S
solution (thiourea) and optionally 5-10% of the additional complexing
agent solution (TEA), the balance being the solvent, i.e. water.

[0178] Furthermore, those of skill in the art will recognize that any of
the embodiments of the present invention can be applied to almost any
type of solar cell material and/or architecture. For example, the
absorber layer in solar cell 10 may be an absorber layer comprised of
silicon, amorphous silicon, organic oligomers or polymers (for organic
solar cells), bi-layers or interpenetrating layers or inorganic and
organic materials (for hybrid organic/inorganic solar cells),
dye-sensitized titania nanoparticles in a liquid or gel-based electrolyte
(for Graetzel cells in which an optically transparent film comprised of
titanium dioxide particles a few nanometers in size is coated with a
monolayer of charge transfer dye to sensitize the film for light
harvesting), copper-indium-gallium-selenium (for CIGS solar cells), CdSe,
CdTe, Cu(In,Ga)(S,Se)2, Cu(In,Ga,Al)(S,Se,Te)2, Cu--In, In--Ga,
Cu--Ga, Cu--In--Ga, Cu--In--Ga--S, Cu--In--Ga--Se, other absorber
materials, II-VI materials, IB-VI materials, CuZnTe, CuTe, ZnTe,
IB-IIB-IVA-VIA absorbers, or other alloys, other absorber materials,
IB-IIB-IVA-VIA absorber solar cells, other thing film solar cells, and/or
combinations of the above, where the active materials are present in any
of several forms including but not limited to bulk materials,
micro-particles, nano-particles, or quantum dots. The CIGS cells may be
formed by vacuum or non-vacuum processes. The processes may be one stage,
two stage, or multi-stage CIGS processing techniques. Additionally, other
possible absorber layers may be based on amorphous silicon (doped or
undoped), a nanostructured layer having an inorganic porous semiconductor
template with pores filled by an organic semiconductor material (see
e.g., US Patent Application Publication US 2005-0121068 A1, which is
incorporated herein by reference), a polymer/blend cell architecture,
organic dyes, and/or C60 molecules, and/or other small molecules,
micro-crystalline silicon cell architecture, randomly placed nanorods
and/or tetrapods of inorganic materials dispersed in an organic matrix,
quantum dot-based cells, or combinations of the above. Many of these
types of cells can be fabricated on flexible substrates.

[0179] Additionally, concentrations, amounts, and other numerical data may
be presented herein in a range format. It is to be understood that such
range format is used merely for convenience and brevity and should be
interpreted flexibly to include not only the numerical values explicitly
recited as the limits of the range, but also to include all the
individual numerical values or sub-ranges encompassed within that range
as if each numerical value and sub-range is explicitly recited. For
example, a thickness range of about 1 nm to about 200 nm should be
interpreted to include not only the explicitly recited limits of about 1
nm and about 200 nm, but also to include individual sizes such as but not
limited to 2 nm, 3 nm, 4 nm, and sub-ranges such as 10 nm to 50 nm, 20 nm
to 100 nm, etc.

[0180] The publications discussed or cited herein are provided solely for
their disclosure prior to the filing date of the present application.
Nothing herein is to be construed as an admission that the present
invention is not entitled to antedate such publication by virtue of prior
invention. Further, the dates of publication provided may be different
from the actual publication dates which may need to be independently
confirmed. All publications mentioned herein are incorporated herein by
reference to disclose and describe the structures and/or methods in
connection with which the publications are cited. For example, U.S.
patent application Ser. No. 61/333,241 filed May 10, 2010 is fully
incorporated herein by reference for all purposes.

[0181] While the above is a complete description of the preferred
embodiment of the present invention, it is possible to use various
alternatives, modifications and equivalents. Therefore, the scope of the
present invention should be determined not with reference to the above
description but should, instead, be determined with reference to the
appended claims, along with their full scope of equivalents. Any feature,
whether preferred or not, may be combined with any other feature, whether
preferred or not. In the claims that follow, the indefinite article "A",
or "An" refers to a quantity of one or more of the item following the
article, except where expressly stated otherwise. The appended claims are
not to be interpreted as including means-plus-function limitations,
unless such a limitation is explicitly recited in a given claim using the
phrase "means for."